4 June 2019
Encouraging news for patients with metastatic estrogen receptor-positive (ER+), Her2/neu negative breast cancer was presented at the 2019 American Society of Clinical Oncology annual meeting, and published in the New England Journal of Medicine.
The MONALEESA-7 Phase III trial evaluated the use of ribociclib in combination with endocrine therapy. Patients who received ribociclib and endocrine therapy were found to have improved overall survival rates compared to those who received endocrine therapy alone. Prior studies demonstrated improved progression free survival, but this was the first demonstration of an improvement in overall survival. Patients enrolled in this study were pre- or peri-menopausal.
Ribociclib is an oral medication belonging to the CDK 4/6 inhibitor class of targeted agents. The CDK 4/6 pathway is important for cell division. CDK 4/6 inhibitors block progression through the normal cell cycle, so cancer cells are “arrested” in a resting phase and cannot divide. This study found that at 42 months, patients treated with ribociclib had a 70% overall survival rate, compared to 46% for the patients who received endocrine therapy alone. In absolute numbers, there were 26 fewer deaths (83 or 337 versus 109 of 335) in the treatment group. Because patients who develop metastatic breast cancer after a diagnosis of early-stage disease are not re-staged, it is not possible to determine with certainty how many patients this medication may be appropriate for. Approximately 40,000 women and 500 men die from metastatic breast cancer every year. ER+ is the most common breast cancer subtype.
Prior studies have evaluated a similar drug, palbociclib, which has been approved for use in women and men with metastatic breast cancer. There are ongoing studies evaluating all 3 of the “ciclib” agents to get a better sense of whether the results will be similar across all patient populations or if a particular drug will be better for a particular subset of patients. All 3 agents are oral (pills). While side effects may be an issue for some patients, these medications are much better tolerated compared to traditional chemotherapy. Unfortunately, cost and insurance coverage may be an issue in some situations.
In addition, I do think that it is important to point out that in the current study, the majority of patients (67% in the ribociclib arm and 73% in the endocrine therapy alone arm) went on to receive other therapy – meaning that the disease progressed. We are still a long way from a “cure” despite improvements in overall survival, and we’re a long way from single-agent therapy in patients with metastatic breast cancer. Patients with metastatic breast cancer are still expected to need more than one, and in some cases multiple, agents over time as the cancer finds ways to mutate and continue to grow. The findings of this study are a step in the right direction, but much more research is needed.