Abstract PO4-05-11: Effects of body mass index on the treatment outcome of patients with metastatic breast cancer in the real world

Abstract Purpose: Metastatic/recurrent breast cancer has a relatively long survival compared to other cancers and depending on the biologic subtype, the treatment outcome is different. In general, obesity or overweight is associated with poor prognosis of breast cancer, but the relationship between body mass index (BMI) and prognosis in metastatic cases is not clear. The aim of this study is investigating the effect of BMI on survival outcome through long-term follow-up in single institution, retrospectively. Method: This study included the patients with metastatic/recurrent breast cancer who has been diagnosed from January 2000 to December 2022 in an institution. BMI was calculated based on weight at diagnosis of metastatic disease, divided into 4 groups according to Asian-Pacific classification, and clinical characteristics including biologic subtype and overall survival (OS) were retrospectively reviewed. The statistical analysis was performed using Kaplan-Meier survival analysis and Cox proportional hazard model. Result: A total of 679 patients were enrolled. Median age was 51 years-old (25~89), 672 patients (99.0%) were female and 425 patients (62.6%) showed pre-menopausal status. The frequencies of HR+, HER2, and TNBC subtype were 335 (50.7%), 191 (28.9%), and 135 (20.4%), respectively and the BMI classification was 33 (5.5%), 251 (41.6%), 124 (20.5%), 196 (32.4%) for underweight, normal, overweight, and obesity, respectively. During a median follow-up of 33.8 months, the median OS in each of the HR+, HER2+, and TNBC subgroups was 54.9 (95% CI 38.7-71.1), 62.8 (95% CI 47.8-77.8), and 20.8 months (95% CI 12.0-29.7). In univariate analysis, there was no statistically significant difference in OS according to BMI in whole patients, however, in the HER2-positive group, the underweight BMI group showed poor OS (p=0.045). In multivariate analysis, the factors affecting OS were age (HR 0.59, 95% CI 0.41-0.87, p=0.008), poor ECOG PS (HR 8.35, 95% CI 2.54-27.49, p 0.001), TNBC subtype (HR 2.14, 95% CI 1.56-2.94, p 0.001), visceral metastasis (HR 2.13, 95% CI 1.63-2.79, p 0.001), 5% or more weight loss during treatment (HR 1.46, 95% CI 1.09-1.97, p=0.012) and obesity BMI group (HR 0.69, 95% CI 0.51-0.94, p=0.019). Conclusion: In the case of patients with metastatic/recurrent breast cancer, there is concern about an increase in body weight, a known risk factor for breast cancer, while receiving palliative aim treatment. For the past 20 years, the mainstay of treatment for metastatic/recurrent breast cancer has been cytotoxic chemotherapy or anti-HER2 agents, and in this case, the higher BMI group patients showed better treatment outcomes compared with normal BMI patients. Citation Format: Kyoung Eun Lee, Ahrong Ham, Sewon Lee, Jungmin Jo, Soo Ji Hong, Ji Eun Lee, Haena Lee, Sungchan Gwark, Jeongshin An, Hyun-Goo Kim, Jun Woo Lee, Joohyun Woo, Woosung Lim, Byung-In Moon, Sei Hyun Ahn, Hye Ah Lee. Effects of body mass index on the treatment outcome of patients with metastatic breast cancer in the real world abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-05-11.