Rethinking endpoints for anti-obesity pharmacotherapy in patients with hr+ early breast cancer receiving endocrine therapy: from body weight and BMI to body composition

INTRODUCTION: Body weight (BW) and body mass index (BMI) are commonly used to assess obesity and response to weight-management interventions in patients with hormone receptor-positive (HR+) early breast cancer (eBC) receiving endocrine therapy. However, these measures do not adequately reflect changes in fat mass, visceral adiposity, lean mass and sarcopenia-related phenotypes. AREAS COVERED: This focused narrative review examines whether BW and BMI are sufficient endpoints for evaluating obesity management and anti-obesity pharmacotherapy in patients with HR+ eBC receiving endocrine therapy. PubMed and ClinicalTrials.gov were searched for relevant evidence until 23 June 2026, including BC-specific studies of obesity pharmacotherapy and registered interventional trials. Studies have reported increases in total and visceral fat mass after adjuvant BC treatment, while changes in lean mass have been less consistent. The identified BC-specific studies remain mainly retrospective and weight-centric, with none assessing body composition as a key outcome. EXPERT OPINION: BW and BMI may be useful entry and monitoring variables, but insufficient as stand-alone endpoints. Body composition should be considered as a complementary endpoint, alongside metabolic, functional and oncologic outcomes. Future studies should also assess endocrine therapy adherence and persistence to better characterize the benefits and risks of anti-obesity pharmacotherapy in patients with HR+ eBC.