Background: Body Mass Index (BMI) is a significant prognostic factor in the survival of patients with hormone receptor-positive breast cancer (BC).[1-2] However, the relationship between BMI and survival is not well-established in hormone receptor-negative (HR-) breast tumors. [3] Emerging data is mixed: some studies show that BMI does not impact outcomes in HR- tumors [4], while others reveal worse survival in patients with elevated BMI.[5] In this study, our objective was to corroborate recent evidence about the relationship between BMI and mortality in hormone-negative breast cancer. Methods: We used the PLCO cancer screening trial, a publicly available database containing information about 155,000 participants enrolled in the United States between 1993 and 2001. Data were collected on cancer mortality through 2018 (median follow-up of 19.2 years post enrollment). The methodology of the PLCO trial has been described previously.[6] All female patients with a diagnosis of HR- BC diagnoses were selected for data retrieval, including HR-/HER2+ and HR-/HER2- tumors. Patients with equivocal receptor status were excluded. We used multivariate Cox regression to analyze mortality by BMI category, after adjusting for all significant variables at the bivariate level (p<0.25). Results: 348 women with confirmed HR- BC at the time of study participation were included. Mean age was 69 years old, and 62 patients (17.8%) passed away due to breast cancer during study enrollment or follow-up. Patients who were of normal weight (BMI 25-<30) at age of trial enrollment were not significantly more likely to survive compared to overweight or obese patients (Hazard Ratio 1.274, p= 0.623). Conclusions: Our results show no significant relationship between BMI and mortality in patients with HR- BC tumors. This finding adds to the growing literature about weight status in hormone receptor-negative tumors. Our data suggests that the mechanism of tumor progression in HR- breast tumors is unlikely to involve signaling mechanisms in adipocytes. Clinical trial information: NCT00002540, NCT01696968, NCT01696981, NCT01696994.

* Values are hazard ratios (HR) relative to the reference (obese category, BMI ³30). HRs were adjusted for history of diabetes and tumor stage, factors significant at p<0.25 at the bivariate level. ** Cell number < 5.