The impact of obesity and endocrine therapy on the prognosis of premenopausal women with hormone receptor‐positive breast cancer: A single‐institute retrospective study

Background Higher body mass index (BMI) is associated with worse prognosis in pre‐ and postmenopausal patients with breast cancer (BC). However, there is insufficient evidence regarding the optimal adjuvant endocrine therapy for obese premenopausal women with hormone receptor (HR)‐positive BC. Aim To evaluate the impact of obesity and adjuvant endocrine therapy on prognosis in premenopausal patients with BC. Methods and results We retrospectively reviewed the medical record of premenopausal women who received curative surgery for clinical stage I–III HR‐positive BC from 2007 to 2017. Patients were classified into five groups according to BMI: underweight (UW), normal weight (NW), obese 1 degree (OB1), obese 2 degree (OB2), and obese 3 degree (OB3) categories. The primary analysis was a comparison of BC‐specific survival (BCSS) according to BMI (UW/NW vs. OB1–3) and adjuvant endocrine therapy (with or without ovarian function suppression [OFS]). Of 13 021 patients, the data of 3380 patients were analyzed. BCSS in OB1–3 patients was significantly worse than that in patients with UW/NW (hazard ratio [HR] 2.37; 95% confidence interval [CI], 1.40–4.02: p = .0009). In OB1–3 patients who received tamoxifen (TAM), BCSS was significantly worse than that in UW/NW patients (p = .0086); however, a significant difference was not shown in patients who received TAM and OFS (p = .0921). Conclusion High BMI was associated with worse prognosis in premenopausal patients with HR‐positive BC who received adjuvant TAM. The role of OFS as adjuvant endocrine therapy remains unclear, and further studies are required to explore the adequate management of obese premenopausal patients.