Evaluating the real-world safety and effectiveness of palbociclib and hormonal therapy in patients with advanced breast cancer.

This study investigated whether the combination of hormonal therapy and cyclin-dependent kinase (CDK) 4/6 inhibitor palbociclib (Ibrance) was effective in advanced breast cancer in a real-world practice. The authors found that this treatment has similar safety and effectiveness in these patients as shown in clinical trials. Also, the authors showed that a lower number of neutrophils (a type of white blood cells that fight off infection) may lower the risk of cancer worsening.

Breast cancer (BC) is one of the most common cancers affecting women worldwide. Some BCs can have high levels of a protein called HER2 (human epidermal growth factor receptor 2) on their surface. These are called HER2-positive (+) BCs. When HER2 protein is not present, they are classified as HER2-negative (-) BCs. Other BCs grow in response to the female sex hormones estrogen and/or progesterone. These are called hormone receptor (HR)-positive (+). HR+ BC is usually treated with hormonal therapy such as letrozole (Femara).

In patients with advanced HR+/HER2- BC, the current standard treatment involves a combination of hormonal therapy and CDK 4/6 inhibitor. CDK 4/6 inhibitors, such as palbociclib, abemaciclib (Verzenios), and ribociclib (Kisqali), are drugs able to block the action of the cyclin D1 protein, which is involved in the growth and spread of cancer cells.

A recent clinical trial has shown that the combination of letrozole hormonal therapy and palbociclib improve the survival without cancer worsening in patients with HR+/HER2- BC. However, the most common side effect of this treatment is a low number of neutrophils (neutropenia). Since in clinical trials patients are selected to be fit and otherwise healthy, it is important to evaluate the safety and effectiveness of the combination of hormonal therapy and palbociclib in patients in a real-world practice. 

165 patients with HR+/HER2- advanced BC were evaluated. These patients were treated with palbociclib plus hormonal therapy, mainly letrozole as their first line therapy. The average follow-up time was 17.98 months.

Overall, the average survival without cancer worsening was 24.19 months. Patients with a lower number of neutrophils had a 15% lower risk of cancer worsening. 

This study showed that the combination of hormonal therapy and palbociclib improves survival without cancer worsening in a similar way as shown in clinical trials. Also, it showed that patients with neutropenia may have a lower risk of cancer worsening.  

Patients in this study used several different hormonal therapies. This might have influenced the results. Also, the study did not look at other medical conditions, dose delay, and reductions, which could affect the outcome.