Abstract Obesity’s impact on breast cancer prognosis may depend on molecular subtype, yet there is limited research on premenopausal women with HR+HER2- breast cancer. In this study, we included 5,094 premenopausal women with HR+HER2- early-stage breast cancer who underwent radical surgery at 42 breast centers across China between 2016 and 2021. Patients were categorized into four BMI groups: underweight (UW), normal weight (NW), overweight (OW), and obese (OB).