While the approval of new agents represents a great step forward in the treatment of chronic lymphocytic leukemia (CLL), physicians are now challenged with how to best utilize these new treatment options, according to a presentation by Anthony Mato, MD, MSCE, at the 2nd Annual Live Medical Crossfire: Hematologic Malignancies.
Anthony Mato, MD, MSCE
While the approval of new agents represents a great step forward in the treatment of chronic lymphocytic leukemia (CLL), physicians are now challenged with how to best utilize these new treatment options, according to a presentation by Anthony Mato, MD, MSCE, at the2nd AnnualLive Medical Crossfire: Hematologic Malignancies meeting presented in New York, NY.
"There have been several molecules that have been approved," said Mato, director of the CLL Program Leukemia Service, Memorial Sloan Kettering Cancer Center. "It is wonderful for providers and patients to have these opportunities, but new challenges have emerged on how to best sequence these therapies, combine these therapies, and how to manage patients who fail all of these therapies either sequentially or in combination."
Treatment for patients with CLL has significantly evolved from the historical standard of initial chemotherapy with chlorambucil. To date, chemoimmunotherapy regimens have been exploring the incorporation of monoclonal antibodies and targeted therapy, including Bruton tyrosine kinase (BTK) inhibitors and novel inhibitors of phosphoinositide 3-kinase (PI3K).
The BTK inhibitor ibrutinib (Imbruvica) in combination with standard frontline chemoimmunotherapy fludarabine/cyclophosphamide/rituximab was explored in a recent phase II study as a frontline treatment for patients with CLL who were young and fit.1Of the 35 patients evaluable for efficacy, the overall response rate (ORR) was 100%. Furthermore, 57% of patients achieved a complete response with bone marrow minimal residual disease (MRD)-negativity and 83% achieved bone marrow MRD-negativity at best response.
In a similar population setting, ibrutinib was also combined with chemoimmunotherapy fludarabine, cyclophosphamide, and monoclonal antibody obinutuzumab (Gazyva) as frontline treatment.2TP53aberrations, however, were excluded from the study and all patients (n = 32) wereIGHV-mutated. The phase II trial showed an objective response rate of 100%, similar to the previous trial, with 87% of patients achieving bone marrow MRD-negativity after 3 cycles of therapy.
"The take home from this evaluation was that early on in therapy, we see 100% ORR, we see a high proportion of patients who are MRD-negative or MRD-undetectable," said Mato. "So [these are] very active combinations."
Other combinations outside of chemoimmunotherapy are also undergoing evaluation. The phase III MURANO study included 389 patients with relapsed/refractory CLL who were randomized to rituximab plus either venetoclax (Venclexta) (n = 194) or bendamustine (n = 195).3
With a 23-month median follow-up, the median progression-free survival (PFS) was not reached in the venetoclax arm compared with 18.1 months (95% CI, 15.8-22.3) in the bendamustine arm (HR, 0.19; 95% CI, 0.13-0.28;P<.0001). Additionally, higher and more durable peripheral blood MRD-negativity rates were obtained with the use of venetoclax and rituximab (Rituxan). Based on these findings, venetoclax was granted a standard FDA approval for patients with CLL following at least 1 prior therapy.
Venetoclax has also proven to be effective in combination with ibrutinib. The phase II CAPTIVATE data demonstrated 100% ORR with the frontline combination.4Of the 164 patients enrolled on the study, 77% of patients tested for MRD-negativity in the peripheral blood after 6 cycles of treatment.
A significant proportion of patients of patients with CLL are treated with ibrutinib in the first-line and relapse/refractory setting, noted Mato. For these patients, the reason for discontinuation greatly influences the choice for next therapy, however, data on sequencing following ibrutinib are limited.
A prospective phase II trial looked at venetoclax as monotherapy in patients with CLL who had discontinued either ibrutinib or idelalisib (Zydelig).5For those who discontinued ibrutinib-based therapy (n = 91), the ORR was 60% (n = 59). Additionally, a durable PFS of 24.7 months was observed.
Additionally, data from a retrospective analysis looked at patients who had discontinued treatment with a BTK inhibitor or venetoclax.6For patients who discontinued B-cell receptor kinase inhibitor (KI) treatment based on toxicity, those treated with an alternative KI showed superior PFS when compared with patients who discontinued treatment based on disease progression.
"The take home here was that reasons for discontinuation may be relevant. For patients who discontinued ibrutinib because of toxicity, they could be rescued with idelalisib, for example. For patients who discontinued ibrutinib in the setting of disease progression, an alternative KI didn't do so well. Those patients were probably best suited for venetoclax-based therapy."
Additional considerations need to be considered in the relapsed/refractory setting, added Mato, including repeated prognostic evaluation. "CLL is not a static disease, it is a disease of genetic instability. You can acquire abnormalities and those may influence treatment decision-making."
For patients treated with chemoimmunotherapy who develop relapsed/refractory disease, re-challenging chemoimmunotherapy is rarely advised based on limited efficacy and potential risks. Instead, preliminary data have shown promise with novel agents, such as ibrutinib, idelalisib, and venetoclax, after failure of frontline treatment.Although monotherapy and combination therapy in the setting of frontline and relapse/refractory CLL are continuing to be evaluted, Mato noted during his presentation that comparative data are lacking. "If all of these drugs are available for me, how can I pick and choose one combination over another? Additionally, we have no data on sequencing, no comparison to sequential monotherapies, which I think is important," said Mato. "If I give everything upfront, is it any better than doing ibrutinib, idelalisib, and venetoclax sequentially? We have no relevant control tests with the exception of the data from the MURANO trial."