BACKGROUND

Tumor infiltrating lymphocytes (TILs) are a promising inexpensive prognostic and predictive biomarker in breast cancer. High levels of TILs are associated with improved survival and higher probability to achieve pathological complete response in triple-negative breast cancer (TNBC).

OBJECTIVE

To assess the level of TILs in TNBC samples and analyze the association between the level of TILs and the main pathological parameters, to identify their impact on long-term results.

MATERIAL AND METHODS

The study included information on 140 patients with I-III stage TNBC and estrogen receptors <10%. Tumor tissue samples at baseline biopsies were evaluated the histological type, HER2 expression, estrogen expression levels, Ki-67 and TILs. The pathological response was evaluated according to the ypTNM, Miller—Payne, and RCB classifications.

RESULTS

The average level of TILs in biopsy specimens before NACT was 29.3±23.1%. Low levels of TILs (<10%) were defined in 21% of cases, intermediate levels (≥10% to ≤40%) in 55% of cases, and high levels (>40%) in 24% of cases. Using the two-tiered system, low TILs (≤40%) were defined in 76% and high TILs (>40%) in 24% of cases. The level of TILs was correlated with histological grade (R=0.187; p=0.027) and estrogen receptor expression level (R=0.211; p=0.012). There were no significant differences depending on the level of TILs and other pathological parameters. Three-year event-free survival (EFS) in patients with high TILs levels was 95% versus 65% in the low TILs group (p=0.037).

CONCLUSION

Stromal TILs are an important prognostic biomarker in TNBC. Using a cutoff of 40%, high TILs are significantly associated with longer EFS.