Preclinical data have provided a strong rationale for the potential clinical utility of poly(ADP-ribose) polymerase (PARP) inhibitors in the management of patients with epithelial ovarian cancer who have known mutations (germline or somatic) in BRCA. Clinical experience, both in the phase II and phase III trial settings, has confirmed substantial biological and clinical activity for this class of antineoplastics in disease management. Further, there is evidence for the utility of PARP inhibitors in ovarian cancers in the absence of BRCA mutations (germline or somatic), presumably resulting from other molecular deficiencies in DNA repair.

There are currently 3 PARP inhibitors approved by the FDA for commercial use, each with different clinical indications. Although these agents appear to have somewhat different toxicity profiles, to date there have been no direct comparisons among the drugs. Ongoing trials in ovarian cancer are exploring additional clinical indications and novel strategies designed to combine PARP inhibitors with other antineoplastics (eg, antiangiogenic agents, checkpoint inhibitors).

There is genuine excitement within the gynecologic cancer clinical and research communities for the potential role of poly(ADP-ribose) polymerase (PARP) inhibitors in the management of ovarian cancer. Since the introduction of paclitaxel into the oncologist&rsquo;s armamentarium more than 20 years ago, there have been a paucity of phase III trial data challenging the existing treatment paradigms, and even where such data exist, they often generate as much controversy as they actually change current thinking regarding current disease management (eg, neoadjuvant chemotherapy, intraperitoneal platinum drug delivery, paclitaxel maintenance treatment). An important exception to this statement are data related to the delivery of bevacizumab in the management of ovarian cancer in several settings, but even here the optimal use of this strategy remains to be defined.

In addition to impressive and provocative trial data (highlighted below), including striking differences between treatment and control arms in several randomized, double-blind, placebo-controlled clinical trials, the observation that there are currently 3 PARP inhibitors approved for routine clinical use in the United States in the management of ovarian cancer is testimony to both the utility of this class of drugs and the realistic potential that these agents will favorably affect the natural history of the malignancy in a substantial proportion of individuals.

Clinical Trials of PARP Inhibitors in Ovarian Cancer

Preclinical data demonstrating that both the BRCA and PARP pathways are critically relevant to the fundamental process of DNA repair, and subsequent studies demonstrating that inhibition of PARP (through the introduction of a drug that interferes with PARP function) produces profound cell kill in cells genetically deficient in BRCA, have resulted in the clinical exploration of the utility of such inhibition in patients with ovarian cancer who have known germline BRCA mutations.

Olaparib, the first PARP inhibitor to be introduced into the clinic for the treatment of ovarian cancer, has been shown in several studies to possess an impressive degree of single-agent activity (approximately 30% to 50% response rate) when employed as a second-line (or later) strategy in the presence of BRCA mutations.

Clinical activity was most commonly noted in the platinum-sensitive patient population, although individuals with platinum-resistant cancers were also documented to respond. Further, clinical activity has also been observed in high-grade serous ovarian cancers in the absence of a BRCA mutation, although the response rates are lower in this setting.

In a subsequently conducted landmark double-blind, randomized phase II trial, patients with high-grade ovarian cancer in a second remission following platinum-based chemotherapy received either olaparib or placebo following discontinuation of the cytotoxic regimen, after attaining an objective response or achieving a state of stable disease.

The study revealed a highly statistically significant improvement in progression-free survival (PFS) (median 8.4 months vs 4.8 months; HR, 0.35; P <.001) in favor of the active treatment. Perhaps of greatest interest, the patient population with a documented germline BRCA mutation experienced almost a tripling of the time to subsequent disease progression (median 11.2 months vs 4.3 months; HR, 0.18; P <.001).

A final report of the long-term follow-up of this study revealed the provocative suggestion for a favorable impact of the maintenance strategy on overall survival.

The preliminary results of a subsequently conducted randomized phase III trial of olaparib compared with placebo in patients with platinum-sensitive recurrent ovarian cancer who were in a complete or partial response after 2 or more lines of platinum-based therapy have recently been reported with a very similar outcome observed.

The overall median PFS for active maintenance therapy versus placebo was 19.1 months versus 5.5 months, respectively (HR, 0.30; P <.001).

Although olaparib is currently approved by the FDA for the single-agent treatment of patients with ovarian cancer with a documented germline BRCA mutation who have received a minimum of 3 prior lines of cytotoxic chemotherapy, it is likely that the recently reported phase III trial data will extend the drug&rsquo;s clinical indications.

Rucaparib, a second PARP inhibitor, has been approved by the FDA for single-agent treatment of women with ovarian cancer who have either a germline or somatic mutation of BRCA and who have received a minimum of 2 prior lines of chemotherapy. The phase II trial data supporting this indication revealed an objective response rate (ORR) of approximately 80% in patients with a BRCA mutation.

In a group of patients treated in the absence of a BRCA mutation and who were characterized as having a high level of loss of heterozygosity, an ORR of 44% was observed. In contrast, in the presence of a low level of loss of heterozygosity, only 20% of treated patients experienced a response.

These data support the hypothesis that defects in DNA repair mechanisms in individual cancers other than BRCA may be appropriate targets for therapy with a PARP inhibitor.

The favorable results of a randomized phase III trial examining the use of rucaparib in the second-line maintenance setting has recently been reported in a press release from the manufacturer of the agent. However, further discussion of the relevance of these data awaits their presentation at an appropriate scientific venue and subsequent publication in the peer-reviewed medical literature.

Niraparib, the third PARP inhibitor available for use in the United States, has specifically been approved for maintenance therapy following the attainment of a second-line (or later) response (complete or partial) to platinum-based chemotherapy. The approval was based on the results of a randomized phase III trial that examined the utility of this agent compared with placebo in this clinical setting.

In women with BRCA-mutation-positive ovarian cancer, the median PFS (following randomization) was 21 months compared with 5.5 months for placebo (HR, 0.27). In the overall nongermline BRCA patient population entered into this study, the median PFS was 9.3 months compared with 3.9 months (HR, 0.45), in favor of niraparib treatment.

Of note in the niraparib trial, similar to the reported experience with rucaparib, a biomarker was evaluated for the purpose of identifying patients whose cancers might be particularly susceptible to this PARP inhibitor despite the absence of a germline

mutation. In fact, in patients without a germline

mutation whose cancers were found to be homologous recombinant deficiency (HRD) positive, maintenance therapy with niraparib resulted in a median 12.9-month PFS compared with 3.8 months (HR, 0.38) with placebo.

However, since even in the absence of the cancer being HRD positive there was a statistically significant improvement in PFS associated with niraparib treatment, the FDA elected to approve the agent for routine administration as a second-line maintenance strategy (following a response to platinum-based treatment) without requiring the use of a molecular biomarker (either BRCA mutation or HRD-positive).&nbsp;

Choice of PARP Inhibitors in Ovarian Cancer

To date, in the absence of any direct trial-based comparison among the 3 commercially available PARP inhibitors or other agents in clinical development, it is not possible to make any definitive statement regarding the relative efficacy or toxicity of the individual drugs. To date, the agents have received regulatory approval for use in different clinical settings, although based on reported trial results, this situation may change in the near future.

Currently available data suggest somewhat different adverse event (AE) profiles for the individual agents. However, the large majority of patients in the nonrandomized and randomized trial experiences for all 3 drugs were found to be able to continue with therapy (as permitted by the protocol) despite documented toxicity following appropriate dose modifications and treatment interruptions (to permit recovery from the AEs).

Considering the fact that currently available PARP inhibitors are oral agents, it is critical to acknowledge the relevance of even low-grade nausea that may seriously interfere with the willingness of an individual patient experiencing such toxicity to continue with the agent. This concern may be particularly relevant in the maintenance setting, in which a patient who is feeling relatively well and is without cancer-related symptoms may have great difficulty considering taking a medication that can result in a meaningful deterioration in quality of life. Therefore, considerable effort needs to be undertaken by the clinical team to attempt to avoid treatment-related emesis as much as possible. In fact, the continued presence of this AE in a patient, despite efforts to control the symptoms, may be a highly appropriate indication to consider the use of an alternative PARP for that individual.

Future Development of PARP Inhibitors in Ovarian Cancer

Ongoing trials are exploring a number of highly clinically relevant questions related to the use of PARP inhibitors in ovarian cancer, including their use as first-line maintenance strategy.

One obvious issue requiring examination is the potential for clinically meaningful noncross-resistance among the currently commercially available (or still investigative) PARP inhibitors. The so-called PARP-after-PARP strategy might be considered in a patient who has failed to respond to 1 PARP agent or who has initially responded but has now progressed.&nbsp;

Alternatively, the question is relevant for maintenance therapy after different lines of platinum-based treatment or nonplatinum cytotoxic agents. For example, 1 PARP agent might be utilized as first-line maintenance, with a different PARP drug employed following a second-line response to a platinum agent and another PARP inhibitor as third-line maintenance.

Other highly clinically relevant questions in ovarian cancer management include the possible addition of a PARP agent to standard platinum-based cytotoxic therapy, or in combination with bevacizumab (currently a standard-of-care agent in the malignancy), or potentially with a checkpoint inhibitor (currently solely an investigative strategy).

In discussions regarding the use of PARP inhibitors in ovarian cancer, it remains relevant to acknowledge the legitimate concern for the potential development of a myelodysplastic syndrome (MDS) or acute leukemia. Fortunately, to date, the data regarding this devastating toxic effectresulting from prior DNA damage because of potent cytotoxic chemotherapy, and the theoretical concern for the clinical consequences of interference with the body&rsquo;s DNA repair mechanisms&mdash;have been very reassuring. The overall risk of MDS and acute leukemia following treatment with a PARP inhibitor appears to be less than 2%, with many patients having received more than 5 years of continuous PARP inhibitor therapy. However, with the durations of treatments anticipated to become even longer, the far greater numbers of patients soon to be receiving such therapy, and the ongoing exploration of additional novel combination strategies employing PARP agents, careful observation and full reporting of this serious event are required.

Lord CJ, Ashworth A. PARP inhibitors: synthetic lethality in the clinic. Science. 2017;355(6330):1152-1158. doi: 10.1126/science.aam7344.

Fong PC, Boss DS, Yap TA, et al. Inhibition of poly(ADP-ribose) polymerase in tumors from BRCA mutation carriers. N Engl J Med. 2009;361(2):123-134. doi: 10.1056/NEJMoa0900212.

Fong PC, Yap TA, Boss DS, et al. Poly(ADP)-ribose polymerase inhibition: frequent durable responses in BRCA carrier ovarian cancer correlating with platinum-free interval. J Clin Oncol. 2010;28(15):2512-2519. doi: 10.1200/ JCO.2009.26.9589.

Audeh MW, Carmichael J, Penson R, et al. Oral poly(ADP-ribose) polymerase inhibitor olaparib in patients with BRCA1 or BRCA2 mutations and recurrent ovarian cancer: a proof-of-concept trial. Lancet. 2010;376(9737):245-251. doi: 10.1016/S0140-6736(10)60893-8.

Gelmon KA, Tischkowitz M, Mackay H, et al. Olaparib in patients with recurrent high-grade serous or poorly differentiated ovarian carcinoma or triple-negative breast cancer: a phase 2 multicentre, open-label, nonrandomised study. Lancet Oncol. 2011;12(9):852-861. doi: 10.1016/S1470-2045(11)70214-5

Kaufman B, Shapira-Frommer R, Schmutzler RK, et al. Olaparib monotherapy in patients with advanced cancer and a germline BRCA 1/2 mutation. J Clin Oncol. 2015;33(3):244-250. doi: 10.1200/JCO.2014.56.2728.

Domchek SM, Aghajanian C, Shapira-Frommer R, et al. Efficacy and safety of olaparib monotherapy in germline BRCA 1/2 mutation carriers with advanced ovarian cancer and three or more lines of prior therapy. Gynecol Oncol. 2016;140(2):199-203. doi: 10.1016/j.ygyno.2015.12.020.

Ledermann JA, Harter P, Gourley C, et al. Olaparib maintenance therapy in platinum-sensitive relapsed ovarian cancer. N Engl J Med. 2012;366(15):1382- 1392. doi: 10.1056/NEJMoa1105535.

Ledermann J, Harter P, Gourley C, et al. Olaparib maintenance therapy in patients with platinum-sensitive relapsed serous ovarian cancer: a preplanned retrospective analysis of outcomes by BRCA status in a randomized phase 2 trial. Lancet Oncol. 2014;15(8):852-861. doi: 10.1016/S1470-2045(14)70228-1.

Pujade-Lauraine E, Ledermann JA, Penson RT, et al. Treatment with olaparib monotherapy in the maintenance setting significantly improves progressionfree survival in patients with platinum-sensitive relapsed ovarian cancer: results from the phase III SOLO2 study. Abstract presented at: 2017 Society of Gynecologic Oncologists Annual Meeting; March 14, 2017; National Harbor, MD. Abstract LBA2.

Swisher EM, Lin KK, Oza AM, et al. Rucaparib in relapsed, platinum-sensitive high-grade ovarian carcinoma (ARIEL2 Part 1): an international, multicentre, open-label, phase 2 trial. Lancet Oncol. 2017;18(1):75-87. doi: 10.1016/ S1470-2045(16)30559-9.

Mirza MR, Monk BJ, Herrstedt J, et al; ENGOT-OV16/NOVA Investigators. Niraparib maintenance therapy in platinum-sensitive, recurrent ovarian cancer. N Engl J Med. 2016;375(22):2154-2164.

Articles

Clinical Articles

There is genuine excitement within the gynecologic cancer clinical and research communities for the potential role of PARP inhibitors in the management of ovarian cancer.

The Current Status of PARP Inhibitors in Ovarian Cancer

About 71% of patients (17 of 24) with chronic lymphocytic leukemia (CLL) exhibited an overall response (complete and/ or partial response) 4 weeks after receiving chimeric antigen receptor (CAR) T cell infusion therapy. The patients received chemotherapy and anti-CD19 CAR T cells at 1 of 3 dose levels (2 x 105, 2 x 106, or 2 x 107 CAR T cells/kg). Nineteen patients experienced disease progression while receiving ibrutinib, 3 were ibrutinib-intolerant, and 2 did not experience progression while receiving ibrutinib. In addition, 6 patients were venetoclax-refractory, and 23 had a complex karyotype and/ or 17p deletion.

Historically, the overall response rate for CLL has been low, and survival of patients who experienced progression while receiving ibrutinib is short; in addition, median overall survival is only 3 months.

Researchers at the Fred Hutchinson Cancer Research Center in Seattle reported a high rate of elimination of CLL from marrow and lymph node response after patients received CAR-T therapy. The findings suggest that measuring genetic traces of cancer cells taken from bone marrow biopsies might be a better indicator of prognosis than the standard lymph-node scan.

&ldquo;It was not known whether CAR T cells could be used to treat these high-risk CLL patients,&rdquo; lead author Cameron Turtle, MBBS, PhD, attending physician, Fred Hutchinson Bone Marrow Transplant Program, said in a statement. &ldquo;Our study shows that CD19 CAR T cells are a highly promising treatment for CLL patients who have failed ibrutinib.&rdquo;

The study expands on the measures used to indicate whether the CAR T-cell treatment is working. Researchers analyzed samples taken from some of the patients&rsquo; bone marrow 4 weeks after the CAR T-cell infusion. The team used immunoglobulin heavy chain deep sequencing, which is akin to a bar code and enables researchers to track cancer cells in the body.

The researchers performed the analysis in 12 of the patients. Seven of the 12 patients had no malignant copies. All patients without malignant copies were alive and free of disease at a median follow-up of 6.6 months after CAR T-cell infusion.

The 24 patients participating in the study ranged in age from 40 to 73 years, with a median age of 61 years. They had received a median of 5 other therapies, with as few as 3 and as many as 9.

The researchers reported that 83% of patients experienced cytokine release syndrome (grade 1-2, 18 patients; grade 4, 1 patient; grade 5, 1 patient) and 8 patients (33%) developed neurotoxicity (grade 3, 5 patients; grade 5, 1 patient). For the most part, the adverse effects (AEs) were reversible, but 2 patients had AEs severe enough to require being admitted to the intensive care unit, and 1 of those patients died.

Turtle CJ, Hay KA, Hanafi L-A, et al. Durable molecular remissions in chronic lymphocytic leukemia treated with CD19-specific chimeric antigen receptor-modified T cells after failure of ibrutinib. [Epub ahead of print] J Clin Oncol. 2017; doi: 10.1200/ JCO.2017.72.8519.

About 71% of patients (17 of 24) with chronic lymphocytic leukemia exhibited an overall response (complete and/ or partial response) 4 weeks after receiving CAR T cell infusion therapy.

Sustained Molecular Remissions Reported in Patients With Relapsed/Refractory CLL After CD19 CAR-T Infusion

Results, published in the Journal of Clinical Oncology, suggest that savolitinib holds promise as a personalized treatment for a subgroup of patients with metastatic PRCC, the researchers from the Dana-Farber Cancer Institute in Boston, said in a statement.

Of the 109 patients treated, 44 (40%) had MET-driven and 46 (42%) had MET-independent PRCC. MET status was undetermined in 19 patients. PRCC may involve activation of this pathway, through either gene amplification or mutations.

The investigators reported that patients with histologically confirmed locally or advanced metastatic PRCC received a once-daily 600-mg dose of savolitinib orally until progression or treatment discontinuation criteria were met.

The objective response rate (ORR) was 7%. When MET status was determined, ORR was 18% in patients with MET-driven PRCC (8 partial responses [PRs]) compared with MET-independent PRCC (0% PR; P = .002). Further, stable disease was achieved in 22 patients (50%) with MET-driven disease and 11 (24%) with MET-independent disease

In addition, the length of time after treatment before the cancer began growing was significantly longer in the MET-driven tumor group: 6.2 months versus 1.4 months. The authors will continue to follow patients to allow further assessment of the difference in progression-free survival and provide data on overall survival.&nbsp;

The investigators reported MET copy number gain (either chromosomal or focal) in 72% of type 1 PRCCs and 46% of type 2 PRCCs, which is comparable with previous reports of MET copy gain in 81% and 46% of type 1 and type 2 PRCCs, respectively.

&ldquo;These data support the hypothesis that savolitinib has antitumor activity in patients with MET-driven papillary renal cell carcinoma,&rdquo; the authors said in the statement. The study &ldquo;identified a defined molecular group and highlights the prevalence of MET-driven disease in this rare population of RCC patients.&rdquo;

The researchers concluded that MET status was more predictive of response to savolitinib in the study than was a classification based on pathology; all partial responders had archival tumor samples that harbored a copy number gain in the MET pathway (HGF, MET, or chromosome 7), some in combination with a MET kinase domain mutation. This suggests that genomic profiling can better identify patients who may respond to savolitinib than can the type 1 or type 2 histologic subtype, adding relevance to the use of genomic profiling in such studies.

Overall, savolitinib was generally well tolerated, with nausea, fatigue, and vomiting reported as the most common adverse events (AEs). These were similar to AEs reported by patients with PRCC who received foretinib, a MET/ VEGFR2 inhibitor in a prior study.

Other AEs occurring in &ge;10% of patients were peripheral edema, increased alanine aminotransferase and aspartate transaminase levels, serum creatinine increase, and decreased appetite.

In the United States alone, about 6400 cases of PRCC are expected to be diagnosed in 2017, compared with a total of 64,000 cases of kidney cancers. The majority of these cancers are classified as clear cell renal cell cancers. PRCC is classified as nonclear cell kidney cancer.

Patients with metastatic papillary renal cell carcinoma have limited therapeutic options, but results of a phase II safety and efficacy study suggest that a small-molecule inhibitor, savolitinib, could help patients with MET-driven disease.

Savolitinib, Small-Molecule MET Kinase Inhibitor, Demonstrates Safety and Efficacy in Phase II Study

In recent years, preclinical studies have demonstrated the potential of radiotherapy to enhance antitumor immune responses when used in combination with checkpoint inhibition immunotherapy. Our retrospective study of 98 patients with advanced nonsmall cell lung cancer treated on the KEYNOTE-001 trial at the University of California, Los Angeles, found that patients who had received previous radiotherapy compared with those who had not received previous radiotherapy had significantly longer progression-free survival and overall survival upon treatment using the anti&ndash;PD-1 antibody pembrolizumab (Keytruda). Additionally, the safety profile of treatment with radiotherapy and pembrolizumab was determined to be acceptable, although close toxicity monitoring is important for management of pulmonary toxicity. While this finding is novel, additional studies will be necessary to translate the current findings into routine clinical use. Furthermore, investigation is underway to elucidate the mechanism behind the synergistic antitumor activities of radiotherapy and immunotherapy, as well as to find the optimal integration of radiotherapy with immunotherapy to improve clinical outcomes.

Nonsmall cell lung cancer (NSCLC) is the leading cause of cancer-related mortality both in the United States and worldwide.

Because standard first-line therapies including surgery, platinum-based chemotherapy, and radiation therapy offer suboptimal rates of disease control, immunotherapy-based approaches offer a promising treatment alternative. Certain tumors exploit the PD-1/PD-L1 pathway by upregulating PD-L1 to inhibit T-cell activity and evade immune-mediated cell death. Therapies that block PD-1/PD-L1 signaling, known as immune checkpoint blockade inhibitors, increase the endogenous antitumor immune response and have shown clinical activity in multiple tumor types, such as NSCLC, melanoma, and renal cell carcinoma.

The KEYNOTE-001 trial demonstrated the safety and efficacy of pembrolizumab (Keytruda), a monoclonal antibody against PD-1, in patients with metastatic NSCLC.

However, responses to immunotherapy, while unprecedented in advanced NSCLC, are still achieved only in less than 20% of patients, highlighting the need to enhance the efficacy of immunotherapy in these patients.

In the present study, Shaverdian et al performed a secondary analysis of 98 patients treated in the KEYNOTE-001 trial at a single institution (University of California, Los Angeles) to compare survival outcomes between patients who had previously received radiotherapy with patients who had not.

The median time of radiotherapy prior to treatment with pembrolizumab was 9.5 months (range, 1.0-106.0). It was found that previous radiotherapy improved the activity of pembrolizumab in patients with advanced NSCLC, as measured by improved progression-free survival (PFS) and overall survival (OS) in patients who had received prior radiotherapy compared with those who had not (4.4 months and 10.7 months, respectively, vs 2.1 months and 5.3 months). Moreover, it was found that patients with prior extracranial radiotherapy had a significantly improved PFS and OS compared with those without prior extracranial radiation therapy (6.3 months and 11.3 months, respectively, vs 2.0 months and 5.3 months), suggesting greater synergy with extracranial radiation therapy. The combination was also associated with an acceptable safety profile with a trend in increase of any pulmonary toxicity and a statistically significant increase in treatment-related pulmonary toxicity. However, there was no increase in grade 3 or higher treatment-related pneumonitis in patients with prior radiotherapy. These findings are consistent with previous preclinical findings that radiotherapy increases the clinical activity of checkpoint inhibition immunotherapy.

Radiotherapy has been shown to stimulate a systemic immune response and ultimately increase tumor recognition and antitumor activity by 3 basic mechanisms: 1) in situ tumor vaccination, 2) T-cell recruitment toward site of irradiated tumor, and 3) increasing tumor cell vulnerability to cytotoxic T cells.

Tumor irradiation induces immunogenic cell death through activation of dendritic cells and subsequent antitumor T-cell activity. Upon exposure to ionizing radiation, tumor cells release apoptotic bodies that act as tumor-associated antigens, as well as damage-associated molecular patterns, which function in danger signaling to the immune system. Together, these processes lead to increased priming and activation of new antitumor T cells, converting the irradiated tumor to an in situ vaccine.

Radiotherapy also triggers the release of T-cellattracting cytokines and cell surface receptors, recruiting additional effector T cells to the tumor site.

Additionally, irradiation leads to temporary overexpression of cell surface receptors apoptosis antigen 1 and major histocompatibility complex class I on the tumor cell, increasing vulnerability to T-cell mediated attack.

Radiotherapy in Combination With Immunotherapy

Preclinical studies suggest that radiation therapy and immune checkpoint inhibitors work synergistically to enhance antitumor T-cell immunity, presumably leading to greater clinical response rates than either treatment modality alone. Inhibition of the PD-1/ PD-L1 axis suppresses tumor evasion of T-cellmediated cell death, while irradiation enhances T-cell repertoire diversity, further increasing lytic activity of cytotoxic T cells.

Additionally, some studies have observed an abscopal effect (abscopus means &ldquo;away from the target&rdquo;) when combining radiotherapy and immunotherapy; sustained anti-tumor responses were observed outside the site of irradiation.

Despite the compelling evidence for a synergy in antitumor effects with the combination of radiotherapy and immunotherapy, there is currently a paucity of clinical evidence to validate these preclinical findings, and thus the combination warrants further investigations.

Results: Pembrolizumab With or Without Prior

Pembrolizumab With or Without Prior Radiotherapy

Our primary objective was to determine whether previous radiation therapy affected PFS, OS, and pulmonary toxicity in patients with advanced NSCLC on treatment with pembrolizumab. Between May 2012 and July 2014, 98 patients with metastatic NSCLC were enrolled and treated in the phase I KEYNOTE- 001 trial at the University of California, Los Angeles; 1 patient was lost to follow-up. Nine (9%) of 97 patients received 2 mg/kg pembrolizumab every 2 weeks, 35 (36%) patients received 10 mg/kg pembrolizumab every 2 weeks, and 53 patients (55%) received 10 mg/kg pembrolizumab every 3 weeks. Median patient age was 65 years (range, 32-83 years). Forty-two (43%) patients had previously received some radiotherapy for treatment of NSCLC before the first cycle of pembrolizumab. Of the 42 patients, 38 received extracranial radiotherapy and 24 received thoracic radiotherapy. Patients with prior radiotherapy had a median 25.9 months (range, 2.6-107.0 months) between initial diagnosis and treatment with pembrolizumab and had received a median of 3 (0-5 therapies) previous unique systemic therapies, while patients with no prior radiotherapy had a median of 17.3 months (range, 0.9-98.2 months) between initial diagnosis and treatment with pembrolizumab and had received a median of 2 (0-5 therapies) previous unique systemic therapies. Eight (19%) patients with prior radiotherapy had a history of central nervous system (CNS) metastases, and 0 patients with no prior radiotherapy had a history of CNS metastases. Baseline patient characteristics are in TABLE 1.

Both PFS and OS were significantly longer in patients with prior radiotherapy compared with patients who had not received any prior radiotherapy, with a median PFS of 4.4 months (95% CI, 2.1-8.6 months) versus 2.1 months (95% CI, 1.6-2.3 months) and a median OS of 10.7 months (95% CI, 6.5-18.9 months) versus 5.3 months (95% CI, 2.7-7.7 months). PFS was determined using Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. In a separate analysis of non-CNS radiotherapy only, 38 (39%) of 97 patients received extracranial radiotherapy, and both PFS and OS were significantly longer in these patients compared with patients with no prior extracranial radiotherapy, with a median PFS of 6.3 months (95% CI, 2.1-10.4 months) versus 2.0 months (95% CI, 1.8-2.1 months) and a median OS of 11.6 months (95% CI, 6.5-20.5 months) versus 5.3 months (95% CI, 3.8-8.5 months). This separate analysis was done because the blood-brain barrier may isolate the CNS from the systemic immune system, masking the effect of CNS radiotherapy.

In addition to improved survival outcomes, we also found an acceptable safety profile for previous radiotherapy followed by pembrolizumab administration, with a trend in increase of any pulmonary toxicity, a statistically significant increase in treatment-related pulmonary toxicity, but no increase in serious treatment-related pulmonary toxicity defined as grade 3 or higher pneumonitis.

Fifteen (63%) of 24 patients who previously received thoracic radiotherapy experienced some pulmonary toxicity versus 29 (40%) of 73 patients with no previous thoracic radiotherapy (P = .052), and 3 (13%) patients with previous thoracic radiotherapy had treatment-related pulmonary toxicity versus 1 (1%) patient among those without (P = .046). Significant pulmonary toxicities defined as grade 3 or higher treatment-related pneumonitis occurred in 1 (4%) of 24 patients with previous radiotherapy and 1 (1%) of 73 patients with no previous radiotherapy (P = .44).

Efficacy and Safety of Pembrolizumab With Prior Radiotherapy

Our findings point to the possibility of a synergy between radiation therapy and immunotherapy, which is particularly important for therapeutic agents such as pembrolizumab that already have a relatively low response rate (approximately 20%

) in unselected patients. The level of response to antiPD-1 therapy is correlated with high PD-L1 expression, defined as PD-L1 expression on at least 50% of tumor cells

; however, high PD-L1 expression is found in only one-fourth of patients with advanced NSCLC.

Notably, in the present study, 12 (22%) patients with no previous radiotherapy had PD-L1 expression >50%, versus only 5 (12%) patients with previous radiotherapy who did. Yet patients with previous radiotherapy demonstrated significantly longer PFS and OS despite lower PD-L1 expression, suggesting that radiation may boost the response rate of pembrolizumab among traditional nonresponders. Of note, although patients with prior radiotherapy had significantly more lines of previous systemic treatments and a significantly longer time interval between initial diagnosis and receipt of pembrolizumab, neither factor predicted for PFS. These data and other predictors of PFS and OS are in Table 39 and Table 4.9 Therefore, we attributed the improved clinical outcomes among patients who received previous radiotherapy to enhanced radiation-induced priming of the antitumor immune response, which therefore allowed for greater clinical activity of immune checkpoint blockade with pembrolizumab.

These findings also demonstrate the importance of close toxicity monitoring when combining radiotherapy and immunotherapy. Patients with prior thoracic radiotherapy were found to be at greater risk for any-grade pulmonary toxicity, although the incidence of high-grade pulmonary toxicity did not differ between patients with and without previous thoracic radiotherapy. High-grade pneumonitis, a shared toxicity of antiPD-1 therapy and radiotherapy, is of particular concern for patients with advanced NSCLC whose underlying condition and tumor burden already compromise baseline lung function.

Although all-grade pneumonitis during antiPD-1 monotherapy is relatively rare in patients with NSCLC (estimated incidence of 4.1%), clinicians must be mindful of management strategies to optimize outcomes of combinatorial radiotherapy and immunotherapy.

Prospective clinical trials are necessary to find the optimal dosing and fractionation schedule for radiotherapy, as well as the timing and sequencing of the 2 treatment modalities in order to potentiate the observed effect. Some studies suggest that antiPD-1 administration concurrent with or immediately following radiotherapy maximizes the antitumor immune response

; however, in our present study, radiotherapy was administered a median of 9.5 months (range, 1.0-106.0 months) before the first cycle of pembrolizumab, suggesting the generation of a long-lived immune response. Although our study is limited by its retrospective nature, results of prospective trials would not be available for several years. Our findings urge for continued rigorous investigation in this field to accelerate our efforts at improving outcomes of cancer therapeutics. Currently, various prospective trials evaluating the combination of radiotherapy and immunotherapy are under way (Table 5). One such ongoing trial is the phase I/II NCT03148327 study, led by Lee, testing the combination of radiotherapy with durvalumab, a PD-L1 antibody, in patients with inoperable early-stage NSCLC (https://clinicaltrials.gov/ ct2/show/NCT3148327).

Extensive preclinical data have demonstrated the exciting potential for radiotherapy to enhance anti-tumor immune responses when used in combination with immunotherapy. Our study results, in which patients with previous radiotherapy experienced significantly longer PFS and OS with pembrolizumab treatment versus those with no previous radiotherapy, corroborate these findings. Further investigation is warranted and underway to better understand how radiotherapy and immunotherapy synergize. This revolutionary therapeutic approach holds great promise, and harmonizing this combination may lead to further improvements in clinical outcomes.

Siegel RL, Miller KD, Jemal A. Cancer statistics, 2017. CA Cancer J Clin. 2017;67(1):7-30. doi: 10.3322/caac.21387.

Garon EB, Rizvi NA, Hui R, et al; KEYNOTE-001 Investigators. Pembrolizumab for the treatment of non-small-cell lung cancer. N Engl J Med. 2015;372(21):2018-2028. doi: 10.1056/NEJMoa1501824.

Robert C, Long GV, Brady B, et al. Nivolumab in previously untreated melanoma without BRAF mutation. N Engl J Med. 2015;372(4):320-330. doi: 10.1056/NEJMoa1412082.

The investigators discuss their findings that demonstrate patients with previous radiotherapy experienced significantly longer PFS and OS with pembrolizumab treatment versus those with no previous radiotherapy.

Synergy of Radiotherapy and Anti-PD-1 Therapy With Pembrolizumab in NSCLC: Is This Perfect Harmony?

Immunotherapy has emerged as a promising strategy for glioblastoma (GBM), a disease that remains universally fatal despite the currently available standard of care. Adoptive T-cell therapy has been shown to produce potent antitumor immunity while obviating the need for traditional antigen presentation and primary immune responses. Chimeric antigen receptors (CARs) are specialized molecules that can be expressed on the surface of T cells, allowing for redirected cytotoxicity against tumor antigens of interest. To date, the application of CAR T cells for GBM has been relatively limited, in large part due to a dearth of well-described tumor-specific antigens that are both homogeneously and frequently expressed. A mutated version of the epidermal growth factor receptor, EGFRvIII, is a constitutively activated tyrosine kinase that is expressed on the surface of GBM and other common neoplasms but is completely absent from all normal tissues. We have recently generated CAR T cells directed against EGFRvIII and reported results from a phase I clinical trial investigating this platform in patients with EGFRvIII-expressing GBM. Our study showed that despite conventional notions of central nervous system &ldquo;immune privilege,&rdquo; EGFRvIII CAR T cells trafficked to intracerebral tumors, leading to successful targeting and eradication of this antigen in the brain. Here, we review our experience with EGFRvIII CAR T cells and highlight important considerations for the clinical translation of this therapy in patients with GBM.

Glioblastoma (GBM) is the most common and most deadly primary malignant brain tumor. Despite aggressive multimodal therapy including surgical resection, radiation therapy, antiangiogenic treatments, and temozolomide chemotherapy, a diagnosis of GBM remains uniformly lethal, with an expected survival of less than 15 months from the time of diagnosis.

In addition to providing only incremental benefit in overall survival, these conventional therapies are also nonspecific and can result in incapacitating damage to systemic tissues as well as adjacent brain tissue. Conversely, the immune system, with its inherent biological specificity, has the theoretical capacity to eliminate tumors while leaving healthy cells intact.

One immunotherapeutic platform that has shown great potential is adoptive cellular therapy, or the infusion of antitumor cytotoxic T lymphocytes (CTLs) for patients with cancer. Tumor-reactive CTLs can either be derived from the patient&rsquo;s tumor itself (eg, tumor-infiltrating lymphocytes) or otherwise engineered to express T-cell receptors (TCRs) with antitumor specificity.

A major drawback of this approach, however, is that TCRs are by nature reliant on interaction with a tumor-associated peptide presented by human leukocyte antigen (HLA) molecules, down-regulation of which is a common mechanism of tumor escape.

In contrast, chimeric antigen receptors (CARs) are highly specialized, recombinant surface molecules that combine the antigen-recognizing variable region of an antibody in tandem with intracellular T-cell signaling moieties (eg, CD3&zeta;, costimulatory signal domains).

As such, CARs have the capacity to bind tumor antigen more avidly than endogenous TCRs, and they do so without the need for classically defined peptide-HLA complex or costimulation. In addition, they may incorporate several downstream pathways that make them less susceptible to host mechanisms of immune suppression, including intracellular sequences that have been shown to enhance T-cell survival and proliferation.

To date, perhaps the most dramatic responses in clinical trials have been for CARs targeting CD19, a cell surface antigen expressed exclusively on the surface of B cells and many B-cell malignancies. In patients with relapsed or refractory B-cell acute lymphoblastic leukemia, treatment with CD19 CAR T cells demonstrated complete response rates of approximately 90%, with sustained remission rates at 6 months of nearly 70%.

Despite successful targeting of CD19 in hematologic malignancies, however, the application of CAR immune therapy to solid tumors has been relatively limited, in large part due to the dearth of tumor antigens that are homogeneously expressed in the setting of malignancy yet are completely absent in healthy tissues. Indeed, given the potent cytotoxicity of CAR T cells, cross-expression of tumor surface antigens in healthy cells can lead to severe &ldquo;off-tumor, on-target&rdquo; autoimmune effects that can vary widely depending on the affected organ tissue.

Toward this end, a tumor-specific mutation of the epidermal growth factor receptor, EGFRvIII, has emerged as an ideal surface target for CAR-T cell technology. EGFRvIII is most frequently seen in patients with GBM, but it is also found in a broad array of other human cancers.

It is derived from an inframe deletion of 801 base pairs from the extracellular domain of the wild-type receptor, which results in the translation of an otherwise absent glycine residue at the fusion junction. This novel domain that stems from the union of normally distant parts of the protein creates an antigenic epitope that is not present in any normal tissues.

Functionally, EGFRvIII has constitutive activity that enhances neoplasticity and confers radiation and chemotherapeutic resistance to tumor cells, which in turn become &ldquo;addicted&rdquo; to its downstream signaling pathways and are unable to survive when this stimulus is removed. The exquisite tumor-specificity of EGFRvIII and its importance in the pathobiology of tumors make the mutation an ideal target for CAR T-cell therapy.

We recently described a systematic approach for the creation and development of a new humanized CAR directed against EGFRvIII.

Using vector backbones based on murine CAR T cells that have already been tested in xenograft GBM models, anti-EGFRvIII antibodies were screened and assayed extensively prior to constructing an EGFRvIII CAR with desired functionality and reactivity, followed by testing for antitumor effects in vitro and in pre-clinical murine studies. These data ultimately led to our opening of a phase I clinical trial of EGFRvIII CAR T cells in patients with residual or recurrent GBM (NCT02209376). In this first-in-human clinical trial, we have found that infusion of CAR-TEGFR-vIII cells was feasible through standard technique

and safe, without evidence of off-tumor toxicity such as cross-reactivity to wild-type EGFR.

No clinical or laboratory signs of systemic cytokine release syndrome were observed, and no off-tumor toxicity occurred. Several patients had post CAR TEGFRvIII surgical intervention, which allowed for tissue-specific analysis of certain endpoints. Specifically, CAR T&ndash; EGFRvIII T cells were demonstrated to traffic to tumor by immunohistochemistry, resulting in subsequent eradication of EGFRvIII in residual lesion, implying successful immunological targeting in the brain. In our study, we used a single intravenous dose of CAR T cells. Other investigators have used multiple doses and administered CAR T cells intratumorally or intrathecally through a catheter in the ventricles. In 1 case, intracranial administration of multiple CAR T&ndash;cell doses directed to the interleukin (IL) 13R&alpha;2 antigen were able to induce a transient but complete regression of metastatic GBM.

Ahmed and colleagues induced at least 1 partial response from a cohort of 17 patients with progressive GBM treated with virus-specific T cells transduced with a CAR directed against the HER2 antigen.

Despite these promising findings, several hurdles to successful translation of CAR T cells for patients with GBM remain. While it is still too soon to conclude on objective clinical benefits in survival, early data suggest that further investigation will be needed for optimal efficacy and durable antitumor responses.

First, despite eradication of EGFRvIII antigen expression following CAR therapy, EGFRvIII-negative tumors persisted in several patients, ultimately leading to disease progression. Analogous observations were also noted in clinical studies of an EGFRvIII peptide vaccine, in which patients achieved significantly prolonged survival but eventually had tumor recurrence owing to outgrowth of EGFRvIII-negative tumor.

On the other hand, early evidence in immune-competent murine models suggests that EGFRvIII CARs, under certain circumstances, may elicit host immunity against additional tumor antigens, thereby protecting against EGFRvIII antigen loss.

Further research will be needed to determine whether this effect is recapitulated in clinical studies.

Another critical factor to consider in the successful clinical translation of an EGFRvIII CAR is the growing consensus that, due to the harsh immune-suppressive environment known to be associated with GBM and other solid tumors, combination therapies may be required to achieve durable antitumor responses. In a HER2-transgenic mouse model of breast cancer, mice treated with anti-HER2 CAR T cells and repeated injections of well-described antibodies for checkpoint blockade showed greater CD8 positive CAR T-cell function, less T-cell exhaustion, and enhanced tumor cell killing.

Recently, in models of renal cell carcinoma, CAR T cells have been designed to secrete immune-modulating antibodies in the tumor milieu to achieve superior antitumor immune responses.

Although this strategy has been shown to have potentially important implications on CAR technology, its efficacy has yet to be explored in patients with brain tumors. Of particular note, if shown to be effective, the ability for CAR T cells to secrete checkpoint inhibitors at the site of tumor antigen expression may have particular relevance to the treatment of GBM, not only where immune checkpoint molecules have been shown to be expressed at high levels

but also where the blood-brain barrier may otherwise inhibit the antibody-mediated blockade.

Overall, our work with the EGFRvIII CAR contributes to the growing body of research committed to discovering a novel therapy for GBM. To date, the success of immune therapy has been modest for the treatment of brain tumors because of several factors, the most prominent of which include the relative dearth of tumor-associated and tumor-specific antigens, the associated immunosuppressive microenvironment, the presence of the blood-brain barrier, and toxicities associated with nonspecific activity. EGFRvIII-specific CARs promise to overcome many of these critical barriers, though further work will be needed to successfully translate this platform for patients with GBM, where the need for effective treatment is great.

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The authors share their experience with EGFRvIII-specific chimeric antigen receptors, which they hope will contribute to the growing body of research committed to discovering a novel therapy for glioblastoma.

2017 August | The Journal of Targeted Therapies in Cancer

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