Evaluating the long-term effectiveness and safety of palbociclib plus fulvestrant treatment in patients with HR+/HER2- advanced BC.

This study evaluated the long-term effectiveness and safety of palbociclib (Ibrance) plus fulvestrant (Faslodex) in patients with hormone receptor-positive (HR+) and HER2-negative (HER2-) advanced breast cancer (BC). The data showed that adding palbociclib to fulvestrant was safe and significantly improved the overall survival over the long-term in 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- BC tests positive for the estrogen and/or progesterone receptor (female sex hormones) 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 such as fulvestrant which acts by decreasing the female hormones.

Palbociclib is a targeted therapy. It blocks CDK4 and CDK6 which are important in regulating the cell cycle and cell growth. Blocking these proteins has been shown to slow the growth of HR+ BC. In a previous study, adding palbociclib to fulvestrant therapy improved the overall survival in patients with HR+/HER2- advanced BC. However, the long-term effectiveness and safety of palbociclib plus fulvestrant treatment in patients with HR+/HER2- advanced BC is not known.

This study involved 521 women with HR+/HER2- advanced BC. Patients were randomly assigned into 2 groups. Group 1 included 347 patients who received palbociclib plus fulvestrant. Group 2 included 174 patients who received placebo plus fulvestrant. The average follow-up time was 73.3 months.

The average overall survival was 34.8 months in group 1 compared to 28 months in group 2. Patients in group 1 were 19% more likely to have a better survival than patients in group 2.

After 6 years, 19.1% of the patients were alive in group 1 compared to 12.9% of the patients in group 2.

In patients that had not previously received chemotherapy for advanced cancer, the average overall survival was 39.3 months in group 1 compared to 29.7 months in group 2. In patients that had previously received chemotherapy for advanced cancer, the average survival was 24.6 months in group 1 compared to 24.3 months in group 2. 

Patients in group 1 were 40% more likely to have a longer survival without cancer worsening compared to group 2. The average survival without cancer worsening was 11.1 months in group 1 compared to 5.4 months in group 2. 

There were no new side effects reported with palbociclib and fulvestrant over a longer follow-up. 

This study concluded that adding palbociclib to fulvestrant was safe and significantly improved the overall survival over the long-term in patients with HR+/HER2- advanced BC.

This study was sponsored by Pfizer Inc., the manufacturer of palbociclib.