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.