Is abemaciclib combined with fulvestrant effective in women with HR positive advanced breast cancer?

This study aimed to compare the effectiveness of the combination of fulvestrant (Faslodex) and abemaciclib to fulvestrant alone in patients with advanced breast cancer.

This study concluded that the combination of fulvestrant and abemaciclib had improved outcomes for patients when compared to fulvestrant alone. 

In advanced breast cancer (ABC) the cancer has spread to the lymph nodes and other tissue in the breast or to other sites in the body. Endocrine (hormone) therapies are a treatment option for ABC that is dependent on hormones such as estrogen for growth (HR positive). They work to lower the levels of or block the production of hormones. Fulvestrant is one type of endocrine therapy. Abemaciclib is a treatment that works to prevent new cancer cells being formed and stop tumor growth by targeting a protein present on cancer cells.

It in not known whether combining fulvestrant and abemaciclib would be more beneficial for ABC patients than fulvestrant alone. 

This study involved 669 patients with ABC who were HR positive and HER2 negative (not dependent on HER2 for growth). These patients had cancer progression after treatment with endocrine therapy.

446 patients received fulvestrant and abemaciclib (combination group). 223 patients received placebo (substance with no active effect) and fulvestrant (fulvestrant group). Progression free survival (time from treatment until disease progression), objective response rate (tumor decreases in size) and adverse events (side effects) were monitored.

Progression free survival was 16.4 months for the combination group, compared to 9.3 months for the fulvestrant group.  

48.1% of the combination group had an objective response compared to 21.3% of the fulvestrant group.

Patients in the combination group were more likely to experience adverse events than those in the fulvestrant group. 86.4% of the combination group experienced diarrhea compared to 24.7% of the fulvestrant group. 45.1% of the combination group experienced nausea compared to 22.9% of the fulvestrant group. 

This study concluded that the combination of fulvestrant and abemaciclib was superior to treatment with fulvestrant alone for ABC patients who progressed while on other endocrine therapy.