On June 3, the results of the MONARCH 2 Phase III trial were presented at the American Society of Clinical Oncology (ASCO) conference, showing a benefit in Progression Free Survival (PFS) of Eli Lilly’s abemaciclib in recurrent metastatic breast cancer. Abemaciclib is the third Cyclin D kinase 4/6 (CDK4/6) inhibitor showing a PFS benefit in metastatic breast cancer patients, after Pfizer’s Ibrance (palbociclib) and Novartis’ Kisqali (ribociclib).

Several presentations at the ASCO conference discussed preference for CDK4/6 inhibitors in metastatic breast cancer patients and if these agents should be administered in first or in later lines of metastatic setting. During a Discussion Session, Dr. Ingrid A. Mayer highlighted that there is no sufficient clinical data favoring a unique therapeutic sequence—with CDK4/6 inhibitors often assumed to become a first-line therapy option—or evidence to support the choice of a particular CDK4/6 inhibitor.

From the MONARCH 2 trial, abemaciclib efficacy was found to be equivalent to previously reported Ibrance data. However, physicians interviewed by GlobalData during the ASCO conference confirmed that the safety profile of Kisqali and Ibrance differs dramatically with abemaciclib, the latter showing a rate of diarrhea above 85% in the MONARCH 2 trial.

GlobalData anticipates that while other CDK4/6 inhibitors will compete intensively in first and second line therapy, the real differentiating value of abemaciclib is based on its single agent efficacy in later lines of therapy. The MONARCH 1 Phase II trial results (Poster #1060) have established the efficacy of abemaciclib as single-agent with anti-tumor activity on a continuous dosing schedule in women with human epidermal growth factor (HER2)-negative and hormonal receptor (HR)-positive metastatic breast cancer who received at least two previous lines of therapy.

Based on a poster presented at the ASCO conference (Abstract #1019), abemaciclib was also evaluated as monotherapy in patients with progressive brain metastasis secondary to HR+ metastatic breast cancer. Preliminary analysis showed that two patients out of 23 (8.3%) showed partial response following treatment with abemaciclib.

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In patients with HER2-positive breast cancer, the randomized Phase II MonarcHER study will evaluate the efficacy and safety of abemaciclib in combination with Herceptin (trastuzumab) and endocrine therapy (Abstract #TPS1109). The trial is planning to recruit 225 postmenopausal women with HER2-positive and HR-positive breast cancer previously treated with a minimum of two previous HER2-targeted-based therapies in the metastatic setting. Based on this trial, the triple regimen including abemaciclib could be positioned after the Perjeta + Herceptin + chemotherapy combination (first line) and Kadcyla (trastuzumab emtansine) (second line).

Further investigation is needed for the use of abemaciclib in monotherapy to evaluate its efficacy as single agent in a randomized trial. However, GlobalData anticipates that in this highly competitive CDK4/6 inhibitors space, the use of abemaciclib in recurrent metastatic breast cancer is likely to be pushed beyond the second-line treatment.