Potential Role of Abemaciclib in Prognostic Breast Cancer Subgroups
An exploratory analysis of combined data from the MONARCH 2 and 3 trials demonstrated that all breast cancer subgroups benefited from the addition of abemaciclib to endocrine therapy, with the largest benefit in patients with poor prognostic factors. Matthew P. Goetz, MD, of the Mayo Clinic in Rochester, Minnesota, and colleagues presented these study findings at the 2017 San Antonio Breast Cancer Symposium (SABCS; Abstract GS6-02). The largest improvements were in patients with liver metastases, progesterone receptor–negative tumors, or high-grade tumors.
The investigators assessed data from 1000 patients across the two studies. By identifying that patients with poor prognostic factors may receive greater benefit from the addition of abemaciclib to endocrine therapy, the investigators suggested treatment strategies may be optimized in the future.
Although all subgroups seemed to benefit from the combination therapy, substantial benefit was noted in poor-prognosis subgroups, with increases in both progression-free survival and objective response rate. In fact, compared with patients with longer treatment-free intervals, those with the shortest treatment-free interval seemed to obtain more of a benefit from the addition of the cyclin-dependent kinase 4 and 6 inhibitor abemaciclib.
MONARCH 2 and 3 enrolled patients with hormone receptor–positive, HER2-negative advanced breast cancer. In MONARCH 2, patients whose disease had progressed while receiving endocrine therapy were treated with abemaciclib/placebo plus fulvestrant. In MONARCH 3, patients were treated with abemaciclib/placebo plus nonsteroidal aromatase inhibitors as initial therapy for advanced disease.