The impact of body mass index on the progression free survival of CDK 4/6 inhibitors in metastatic breast cancer patients

Abstract Purpose Endocrine therapy (ET) plus cyclin-dependent kinase (CDK) 4/6 inhibitors is a standard therapy for patients with hormone receptor (HR)-positive HER-2-negative metastatic breast cancer (MBC). We aimed to investigate the effect of body mass index (BMI) on the progression-free survival (PFS) in hormone receptor (HR)-positive MBC patients who received ET plus CDK4/6 inhibitor in second- and later-line therapy. Methods Patients with metastatic HR-positive breast cancer receiving CDK 4/6 inhibitors from three institutions were enrolled in the study. A total of 116 patients admitted between January 2019 and December 2021 were retrospectively evaluated. The patients were divided into three groups according to BMI level as follows: normal weight (group 1) as 18.5–24.9 kg/m2, overweight (group 2) as 25-29.9 kg/m2, and obese (group 3): ≥ 30 kg/m2. Median duration of follow-up was 10.83 months. Comparisons of PFS and BMI categories were performed with Kaplan-Meier curve and log-rank test. Results The PFS was 9.3 (5.3–13.4) month in normal-weight patients, 11.1 (9.7-12.56) month in obese patients, and could not be reached in overweight patients. This difference was statistically significant (p = 0.02). The best response to CDK 4/6 inhibitor treatment in all BMI groups was partial response (group 1: 48.3%, group 2: 69%, and group 3: 46.7%; p = 0.06). Cardiac, hematological and gastrointestinal side effects were similar in all BMI groups (p > 0.05). Conclusion It was shown that while a normal weight had a negative prognostic effect on survival in patients with metastatic breast cancer, the progression-free survival of overweight patients was found to be longer.