HER2 mutations have been identified as another oncogenic driver in the growing list of actionable targets in non–small cell lung cancer. Based on a mounting body of evidence on the impact of HER2 mutations in lung cancer and the growing focus on personalized medicine, the HER2 receptor has gained focus as a potential target for precision medicine treatments for patients with NSCLC.
HER2mutations have been identified as another oncogenic driver in the growing list of actionable targets in nonsmall cell lung cancer (NSCLC). Based on a mounting body of evidence on the impact ofHER2mutations in lung cancer and the growing focus on personalized medicine, the HER2 receptor has gained focus as a potential target for precision medicine treatments for patients with NSCLC.
The HER2 Receptor
Human epidermal growth factor receptor 2 (HER2; ERBB2) is a member of the tyrosine kinase receptor family, which also includes HER1, HER3, and HER4.1The overexpression of HER2 has been shown to result in oncogenic cell proliferation and transformation in humans.
HER2 has long been implicated in breast and gastroesophageal cancers. Specifically in breast cancer, HER2 amplification is associated with poorer survival outcomes.2
In patients with lung cancer,HER2mutations have been identified as a key driver of disease.1Further, the percentage of lung adenocarcinoma cases harboring HER2 mutations is steadily rising.1,2
“HER2 has such a huge presence in breast, gastric, and other malignancies,” Sarada Krishnamurthy, MD, an independent medical hematologist/ oncologist, said in an interview with Targeted Therapies in Oncology. “Though [HER2-targeted treatments are] evidently in the clinical pipeline, [they have] yet to reach us in clinical practice.”
Results from earlier studies have indicated that HER2 overexpression is observed in approximately 1% to 2% of lung cancer cases (FIGURES 1 and 2), whereas results from more current studies show a range of approximately 6% to 30%.1In a report published by the Cancer Genome Project, sequencing of HER2 in 120 lung tumors showed specific somatic mutations, and the prevalence ofHER2mutations was 4%, all of which occurred in adenocarcinomas. Interestingly, these mutated tumors did not demonstrate HER2 overexpression.3
The Lung Cancer Mutation Consortium (LCMC) is a collective of 16 nationwide leading cancer centers in the United States. Through an LCMC initiative, a study was conducted to analyzeHER2mutations within the patient population with lung adenocarcinoma. Among 920 patients tested forHER2mutations, exon 20 insertions were identified in 3% of patients with lung adenocarcinoma within the LCMC cohort.1In particular, comparatively poorer survival outcomes have been observed in patients with activating exon 20HER2mutations compared with those in other patients with lung adenocarcinomas with oncogenic drivers.4Results of the study also noted that of the 24 patients withHER2-mutant NSCLC, those treated with HER2-targeted therapies had a median survival of 2.1 years compared with 1.4 years for those who did not (P= .48).1
Additional data suggest that tumor models and patients expressingHER2mutations tend to be insensitive to EGFR tyrosine kinase inhibitors (TKIs),5suggesting the need for specific HER2-directed therapies for these patients.
Therapies Targeting the HER2 Receptor in Lung Cancer
Given the past clinical experience of targetingHER2mutations for breast cancers, similar treatment agents are being explored for targetingHER2-mutated lung cancer. In the current treatment landscape, HER2-directed therapies range from monoclonal antibodies to antibodydrug conjugates to small molecule TKIs.2
Trastuzumab (Herceptin) is a recombinant humanized monocolonal antibody directed against the HER2 receptor. In tumor cells that overexpress HER2, trastuzumab binds to the membrane HER2 on the tumor cell and induces antibody-dependent cell-mediated cytotoxicity.6In patients withHER2-mutant advanced NSCLC, trastuzumab has shown a modest benefit in 2 retrospective analyses in previously treated patients withHER2-mutant advanced NSCLC.7,8In a 2013 study, among 3800 patients with NSCLC tested forHER2mutations, alterations were identified in 65 patients (1.7%). In 16 of those patients, HER2-targeted treatments were administered after conventional chemotherapy. With trastuzumab-based therapies (n = 15), a 96% disease control rate was observed.7In a study conducted in 2016, within a cohort of 101 patients from European Union centers, 65 were identified as having received HER2-targeted therapies following conventional treatment and demonstrated an objective response rate (ORR) of 50.9%.8Of those patients, 57 received trastuzumab-based therapy. In the study, trastuzumab was given concomitantly with chemotherapy, and the investigators concluded that when given in combination with chemotherapy, trastuzumab may contribute to better results.
Trastuzumab combination therapies and conjugates are also being explored in several phase II studies. One such study, an open-label phase II study, explored the safety and efficacy of trastuzumab in combination with paclitaxel chemotherapy.9The study met the primary endpoint of tumor response according to RECIST criteria and the ORR was 46% across the study. Furthermore, postprogression tumor biopsies showed an absence of HER2 staining in a majority of study patients, indicating that targeting HER2 with a combination of trastuzumab/paclitaxel is a potentially effective treatment strategy.
A HER2-targeted antibodydrug conjugate, ado-trastuzumab emtansine (T-DM1; Kadcyla) is being investigated in patients withHER2-mutated lung adenocarcinomas in a phase II basket trial.10 The study demonstrated positive results in a small group of 18 patients, with partial responses observed in 8 patients (44%), including 2 previously untreated patients and 4 who had received prior HER2-targeted therapy. The study authors concluded that further study is necessary to confirm a potential benefit.
Results of studies of patients with NSCLC on trastuzumab-based therapies suggest a potential benefit of therapy, which requires further exploration.
Afatinib (Gilotrif) is an inhibitor of the receptor tyrosine kinase (RTK) EGFR family with antineoplastic activity. It functions by selectively and irreversibly binding to and thereby inhibiting epidermal growth factor receptors 1, 2 (including HER2), and 4, and certainEGFRmutations.6In recent publications, the modest efficacy and potential implication of afatinib have been demonstrated in case-based and chart review studies.
In a case report of a previously treated patient with NSCLC harboring an exon 20HER2mutation, off-label use of afatinib therapy was administered. Prior to being treated with afatinib, the patient had failed cytotoxic chemotherapy and treatment with a reversible EGFR inhibitor. One month after therapy initiation, the patient showed rapid radiologic response and remained stable through 4 months of treatment with afatinib.11In an international multicenter retrospective study, 27 patients with metastaticHER2-mutated NSCLC were treated with afatinib. Treatment with afatinib in this patient cohort resulted in partial responses in 11% of patients.12The median overall survival was 23 months with afatinib treatment in the study.
Further investigation of afatinib in this patient population is warranted.
Other Preliminary Agents
Several promising agents targetingHER2mutations in patients with NSCLC are also on the horizon. Though data are currently limited, preliminary results suggest a potential benefit.
TAK-788 is an investigational TKI that has shown selective activity in preclinical studies againstEGFRandHER2mutations. An initial report from a phase I/II, first-in-human, open-label study (NCT02716116) in 34 patients showed that TAK-788 exhibited antitumor activity with an adverse event profile consistent with that of other EGFR TKIs.13Partial responses were observed in 3 of 14 evaluable patients, and 6 experienced stable disease.
Dacomitinib, a second-generation, irreversible EGFR TKI, has also been the focus of several clinical studies, including a phase II trial in patients with stage IIIb/IV lung cancers withHER2mutations and amplifications. Partial responses were observed in 3 of 26 patients withHER2exon 20 mutations, 1 of which lasted for 14 months, although no partial responses were observed in the 4 patients with HER2 amplifications. The results of the study concluded that dacomitinib produced objective responses with specificHER2mutations that justify further study.14
Neratinib (Nerlynx), another RTK inhibitor, is currently approved for use in patients with HER2-positive breast cancer. A small phase II study in 62 patients explored the combined inhibition of HER2 and mTOR in patients withHER2-mutated NSCLC, using a combination of neratinib and temsirolimus (Torisel). Responses were observed in 19% of 43 patients treated with the combination, lasting from 2 to 18-plus months during the study period.15No responses were observed in patients treated with neratinib alone.
Research has shown the value of targetingHER2mutations in NSCLC with various therapies. Despite the smaller-size studies and limitations, treatments such as trastuzumab, afatinib, and other compounds offer promising therapies for patients withHER2-mutated NSCLC. “In clinical research-based protocols that translate to our practice guidelines, we have graduated from EGFR to small molecule targeting but seemingly have let the story of HER2 go by the side line,” Krishnamurthy added. “HER2 offers a potential target for treatment in lung [cancer] and is being studied.