Evaluating the effectiveness of abemaciclib alone or in combination with tamoxifen in patients with HR+, HER2– metastatic breast cancer resistant to hormone therapy.

This study evaluated the effectiveness of abemaciclib (Verzenio) alone or in combination with tamoxifen (Nolvadex) in patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) metastatic breast cancer (BC) resistant to hormone therapy. The data showed that abemaciclib in combination with tamoxifen was more effective in improving the overall survival of these patients.

BC is classified into different subtypes depending on the presence or absence of certain receptors (proteins found on the surface of the cancer cells). HR+ and HER2- is a subtype of BC that tests positive for female sex hormone receptors (such as estrogen and progesterone) and negative for the HER2 protein. This type of cancer accounts for 70% of all BCs. Patients with this subtype of BC commonly receive hormone therapy (HT) like tamoxifen. This acts by decreasing the female hormone estrogen. However, many patients with metastatic BC become resistant to HT. This can be challenging to treat.

Abemaciclib is a biological therapy that targets certain proteins involved in the cell cycle. This slows the rate of cancerous cells spreading. Previous studies have shown that abemaciclib combined with HT improves the outcomes of patients with HR+/HER2- advanced BC. However, the effectiveness of abemaciclib alone or in combination with tamoxifen on overall survival outcomes in patients with HR+/HER2- metastatic BC that are resistant to HT is still unknown.

This study involved 234 women with HR+/HER2- advanced BC. Patients were randomly assigned into 3 groups. Group 1 included 78 patients who received abemaciclib (150mg) plus tamoxifen (20mg). Group 2 included 79 patients who received abemaciclib (150mg) alone. Group 3 included 77 patients who received abemaciclib (200mg) plus loperamide (Imodium) to prevent diarrhea. The average follow-up time was 27.2 months.

The average overall survival was 24.2 months in group 1, 20.8 months in group 2, and 17 months in group 3. Patients in group 1 were 38% more likely to have a better survival than patients in group 3.

The average survival without cancer worsening was 9.1 months in group 1, 7.2 months in group 2, and 7.4 months in group 3. Patients in group 1 were 19% more likely to survive without cancer worsening than patients in group 3.

Overall, 34.6% of the patients in group 1 responded to treatment versus 24.1% in group 2 and 33.8% in group 3.

There were no new side effects reported in the 3 groups. 

This study concluded that abemaciclib in combination with tamoxifen was more effective in improving the overall survival of patients with HR+/HER2- advanced BC resistant to HT compared to abemaciclib alone.

This study was funded by Eli Lilly and Co., the manufacturer of abemaciclib. The patients knew which treatment they were getting, which might affect the conclusions.