Lumpectomy followed by radiation improves survival in HER2 positive and triple-negative breast cancer with high tumor-infiltrating lymphocytes compared to mastectomy alone.

OBJECTIVE: The goal was to compare the 5-year DFS and 5-year OS in patients with early-stage human epidermal growth factor receptor 2 breast cancer (HER2+ BC) and triple-negative breast cancer (TNBC) in relation to the amount of stromal tumor-infiltrating lymphocytes (TILs) after locoregional management by either mastectomy without radiation or lumpectomy and whole-breast radiotherapy (RT). METHODS: This was a retrospective review of HER2+ BC and TNBC patients' charts and histopathology slides with clinical stage of T1-T2 N0 who presented at our facility between January 2009 and December 2019. Locoregional treatment included either mastectomy without RT (M) or lumpectomy with RT (L+R). TILs were assessed by three pathologists using the guidelines of the 2014 TILs working group. A competing risk model and Kaplan-Meier analysis were used to analyze correlations between TILs levels and clinical outcome. RESULTS: We reviewed 211 patients' charts. Of them, 190 proceeded to the final analysis. Patients were split into groups of "low TILs" and "high TILs" based on a 50% TILs cut-off. Of them 26% had high TILs, 48% received RT, 97% received chemotherapy, all HER2+ BC patients received HER2-directed therapy and all HER2+ BC that were also hormone receptor positive (HR+) received endocrine therapy (ET). In patient with low TILs, L+R did not improve outcomes compared to M. Moreover, patients with high TILs had a significant improvement of their DFS and OS with L+R when compared to M. CONCLUSION: The results of our study reflect that a selected group of HER2+ BC and TNBC with elevated TILs, L+R is associated with improvement of 5-year DFS and 5-year OS.