Predicting therapeutic efficacy of endocrine therapy for stage IV breast cancer by tumor-infiltrating lymphocytes

The tumor immune environment not only modulates the effects of immunotherapy, but also the effects of other anticancer drugs and treatment outcomes. These immune responses may be evaluated by measuring tumor-infiltrating lymphocytes (TILs), which has been frequently verified clinically. In the present study, the prediction of the therapeutic effect of endocrine therapy by TILs on stage IV breast cancer was clinically analyzed. Data from 40 patients who underwent endocrine therapy as the initial drug therapy for stage IV breast cancer were used. The correlation between TILs, evaluated according to standard methods, and prognosis, including the efficacy of endocrine therapy, was investigated retrospectively. Patients with ≥50% lymphocytic infiltration were considered to have lymphocyte-predominant breast cancer (LPBC). An analysis of outcomes revealed no difference in progression-free survival (PFS; P=0.171), time to treatment failure (TTF; P=0.054), or overall survival (OS; P=0.641) between the high TIL (>10%) and low TIL (≤10%) groups. Patients with LPBC (≥50%) exhibited a significant prolongation of PFS (P=0.005, log-rank), TTF (P=0.001) and OS (P=0.027) compared with non-LPBC patients. On receiver operating characteristics (ROC) curve analysis, better results were obtained with LPBCs [area under the curve (AUC)=0.700] than with TILs (AUC=0.606). The present findings suggest that a high level of lymphocytic infiltration in the tumor stroma may serve as a predictor of the therapeutic efficacy of endocrine therapy in patients with stage IV estrogen receptor-positive breast cancer.