Impact of endocrine therapy on overall survival in ER negative/PR positive locoregional breast cancer: An analysis of the National Cancer Database.

Abstract

545 Background: Breast cancer expressing PR, but not ER (ER-/PR+) are uncommon, comprising 2–8% of breast cancers, with less known about their characteristics and responsiveness to therapy. The role of adjuvant endocrine therapy (ET) in ER-/PR+ locoregional breast cancer is unclear as these patients have been largely excluded from prospective clinical trials. Despite a lack of data patients are often treated with adjuvant ET due to perceived possible benefit. We used the National Cancer Data Base (NCDB) to assess role of adjuvant ET in ER-/PR + breast cancer. Methods: Using the NCDB, we included adults ≥ 18 and ≤ 70 years old in order to minimize the non-cancer related deaths. We selected only female patients with stage I, II, and III. Patients have received definitive surgery (lumpectomy with radiation or mastectomy) with negative margins. Systemic therapy (ST) was defined as receipt of chemotherapy and/or immunotherapy. We excluded those who had unknown ST status, unknown ET status, unknown HER 2 status, who did not receive definitive surgery and those whose survival time was missing. Patients were stratified into four groups based on HER2 status and receipt of ET. Both Multivariable Cox proportional hazards regression modeling was utilized to determine predictors of overall survival (OS). A propensity score matched cohort was developed based on relevant demographic and clinical factors. The primary endpoint assessed was OS. All analyses were performed using SAS 9.4. Results: We identified 5344 patients (74% were Caucasian, 20% were African American and 6% were others) with ER-/PR+(74% were HER2 - and 26% were HER2 +) locoregional breast cancer (51% were Stage I, 38 % were stage II and 11% were stage III). Grade 1 cancer was seen in 2%, grade 2 in 18%, and majority being grade 3 in 80%. Of which 3093 (58%) patients received ET and 4462 (83%) received ST. Majority of patients were in age group 50-70 comprising of 69% patients, 8 % in age 18—39, 23% in age 40-49 with Charlson-Deyo Score of 0 in 83%, 1 in13%, 2-3 in 4%. In a propensity matched cohort (N=3980), ET was not significantly associated with OS among HER2 negative (HER2-) patients (HR=1.05, 95% CI 0.86-1.28, p=0.63). In HER2+ patient ET was associated with significantly improved OS (HR=0.65, 95% CI 0.42-0.99, p=.047). Conclusions: Receiving ET was not associated with improved OS in locoregional ER-/PR+/HER2- breast cancer based on our study using a propensity matched cohort in the NCDB. However, was frequently administered. Interestingly, improved OS was seen in locoregional ER-/PR+/HER2+ breast cancer with adjuvant ET.