Abstract P3-12-14: Attenuated negative prognostic effect of progesterone receptor negativity in postmenopausal ER+ breast cancer with normal BMI (<25): A nation-wide study in Korean Breast Cancer Society and the institutional cohort

Abstract

Abstract Purpose Loss of progesterone receptor (PR) expression is a poor prognostic factor in ER+/HER2- breast cancer. A growing body of evidence suggests that PR expression is affected by endogenous estrogen level and modulated by body mass index (BMI). Using Korean Breast Cancer Society Registry (KBCSR) and institutional database, we evaluated survival outcome by PR expression in the postmenopausal groups stratified by BMI. Moreover, we investigated 21-gene recurrence score to assess intrinsic tumor biology. Method Data from the KBCSR for patients diagnosed with invasive breast cancer when aged over 50 years were reviewed, and 33,314 with BMI were included. Of these, we investigated overall survival (OS) of women at age of 60 and older with a median follow-up of 56 months (n=9,492). In the institutional cohort with ER+HER2- breast cancer women at age of 50 and older (n=703), the landmark survival analyses were performed to address the 5-years recurrence-free survival (RFS). In the subset of the institutional cohort, 21-gene recurrence scores were identified in individuals (n=470). Normal weight is defined as BMI less than 25kg/m2. Result Among the postmenopausal women from the KBCSR, the PR- was significantly associated with adverse OS (hazard ratio [HR], 1.39; 95% CI, 1.16-1.67; p<0.001) in high BMI group (≥25) whereas in normal BMI group (<25) did not (HR, 1.07; 95% CI, 0.89-1.29; p=0.498) (interaction p=0.046). In the institutional cohort with ER+/HER2- postmenopausal women (age>50), RFS was superior in the PR+ than in the PR- in the postmenopausal with high BMI (≥25). In contrast, RFS was not separated by PR in the normal BMI group (<25). When we compared the 21-gene recurrence score according to PR, the scores were significantly lower in the PR+ than in the PR- regardless of BMI. Conclusion In ER+/HER2- aged postmenopausal breast cancer women with normal BMI who have low estrogen environment, negative prognostic effect of absence of PR expression is attenuated. Bad tumor biology of PR- cancer is conserved irrespective of BMI. We support the hypothesis that weight control to reduce endogenous estrogen produced by adipose tissue is beneficial for postmenopausal women with ER+ breast cancer. Citation Format: Soong June Bae, Jawon Hwang, Janghee Lee, Jung Hwan Ji, Chihhao Chu, Jee Hung Kim, Sung Gwe Ahn, Joon Jeong. Attenuated negative prognostic effect of progesterone receptor negativity in postmenopausal ER+ breast cancer with normal BMI (<25): A nation-wide study in Korean Breast Cancer Society and the institutional cohort [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-14.