Tumor Infiltrating Lymphocytes in Breast Cancer Patients with Progressive Disease during Neoadjuvant Chemotherapy

A minority of breast cancer (BC) patients progress during neoadjuvant chemotherapy (NCT). The aim of this study was to assess the value of Tumor infiltrating lymphocytes (TILs) in such a high-risk population where valid biomarkers are eagerly needed. A retrospective review identified BC patients who either progressed during NCT or achieved a pathologic complete response (pCR). An experienced BC pathologist semi-quantified stromal TILs in pre-treatment core biopsies using hematoxylin and eosin stained slides. The primary outcome was to compare the levels of TILs between the 2 groups as a continuous and categorical variable using the t-test and X² test as appropriate. The secondary outcome was to compare survival outcomes between patients with high versus low TILs level using the log-rank test. Fifty patients were successfully identified and assessed for TILs: 21 progressed during NCT and 29 had a pCR. Patients with progressive disease were older with more advanced disease (p = 0.03, p = 0.0001 respectively). A significantly lower mean level of TILs was found in patients with progressive disease compared to patients with pCR: 14.3% (Standard Deviation (SD): 16.9) versus 32.8% (SD: 31), p = 0.01). The level of TILs was neither associated with baseline characteristics nor with survival outcomes. BC patients progressing during NCT have low TILs levels compared to patients with pCR. Prospective studies are needed to establish the utility of TILs as early biomarkers of tumor response, particularly in patients with disease progression who need novel treatment approaches.