Evaluation of the prognostic value of tumor-infiltrating lymphocytes in triple-negative breast cancers

Tumor-infiltrating lymphocytes (TILs) may be associated with clinical outcome in triple-negative breast cancers (TNBCs). However, lacking of standardized methodologies in TILs evaluation has hindered its application in clinical practice. To evaluate the prognostic role of TILs scored by methods recommended by International TILs Working Group 2014, we performed a retrospective study of TILs in 425 primary invasive TNBCs in a Chinese population with a median follow-up of 4 years. Intratumoral TILs (iTILs) and stromal TILs (sTILs) were scored respectively. The associations between TILs and disease-free survival (DFS), distant disease-free survival (DDFS) and overall survival (OS) were evaluated with COX models. ITILs were not associated with prognosis. Higher sTILs were associated with better prognosis; for every 10% increase in sTILs, a 5% reduction of risk of recurrence or death (P < 0.001), 5% reduction of risk of distant recurrence (P < 0.001), and 4% reduction of risk of death (P = 0.002) were observed. Multivariate analysis confirmed sTILs to be an independent prognostic marker. 3.5% of TNBCs had more than 50% lymphocytes (lymphocyte-predominant breast cancer, LPBC), and associations between LPBC status and prognosis were observed but did not reach statistical significance. TNBCs with more than 20% sTILs had a significantly better prognosis than the patients with no more than 20% sTILs. In conclusion, our study indicated that sTILs scored by methods recommended by International TILs Working Group 2014 were associated with the prognosis of TNBCs. STILs could be an independent prognostic biomarker in TNBCs, increasing sTILs predicting better prognosis.