Impact of low estrogen- and progesterone-receptor expression on survival outcomes in breast cancers previously classified as triple-negative breast cancers.

Abstract

1023 Background: Estrogen and progesterone receptor (ER/PR) expression is a fundamental prognostic and predictive marker for breast cancer. Conflicting thresholds for ER/PR positivity have resulted in uncertainty regarding endocrine therapy for low levels of ER/PR (1−10%). The purpose of our study was to evaluate the prognostic significance of low levels of ER/PR on survival outcomes in tumors previously defined as triple-negative breast cancers (TNBC). Methods: We reviewed records of 1257 patients with TNBC (defined as ER/PR < 10% and HER2 negative) followed between 1990 and 2009 at a single institution. Tumors were categorized according to ER/PR expression by immunohistochemistry into one of three groups: ER/PR <1% (Group A), ER/PR 1−5% (Group B) and ER/PR 6−10% (Group C). Kaplan-Meier product limit method was used to estimate recurrence-free survival (RFS) and overall survival (OS). Cox proportional hazards models were fit to determine the association between ER/PR expression and survival, after adjustment for other patient and disease characteristics. Results: Median age was 51 years (range 21 to 98 years). Groups A, B and C had 897 (71.4%), 241 (19.2%) and 119 (9.4%) patients, respectively. Group A had a larger proportion of grade III tumors (P = 0.001). At a median follow up of 44 months, there were 465 recurrences and 367 deaths. The 3-year RFS rates were 64%, 67% and 77% in groups A, B and C, respectively (P=0.34). Corresponding, 3-year OS rates in group A, B and C were 79%, 81% and 88% (P=0.33). ER/PR expression was not an independent predictor for RFS (Group B: HR: 1.11, 95% CI: 0.88−1.41, P=0.37 and Group C: HR: 0.92, 95% CI: 0.65−1.30, P=0.64) or OS (Group B: HR: 1.10, 95% CI: 0.84−1.44, P=0.47 and Group C: HR: 0.88, 95% CI: 0.60−1.31, P=0.54) when compared with Group A. A subset analysis among 118 patients within the three groups who received endocrine therapy showed no significant difference in RFS (P = 0.10) or OS (P = 0.45). Conclusions: In this cohort of TNBC patients, low levels of ER/PR (1−10%) expression appear to have no significant impact on survival outcomes. The benefit from endocrine therapy in tumors with ER/PR 1−10% is uncertain.