Crosstalk Between Programmed Death Ligand 1, Ki-67 Labelling Index, and Tumor-Infiltrating Lymphocytes in Invasive Breast Cancer and Clinicopathological Correlations in a Tertiary Care Center in Western India.

Background & Objective: Breast cancer is the leading cancer among Indian women and accounts for about 25% of all cancer cases worldwide. The present study aimed to assess Programmed Death Ligand-1 (PD-L1) expression in tumoral cells and tumor-infiltrating lymphocytes (TILs) and evaluate their correlations with the Ki-67 labelling index in invasive breast carcinomas (IBC).

Methods: This descriptive observational study was conducted during 2016-2018 and included all diagnosed cases of IBC. The relationships between PD-L1 expression, TILs, hormone receptors, Ki-67, and clinicopathological parameters were studied in IBC. Statistical analysis was performed by SPSS version 23.

Results: Out of 114 evaluated cases, 33.33% (N=38) showed PD-L1+ expression in tumor cells and 47.37% (N=54) had PD-L1+ expression in TILs. A high Ki-67 index was observed in 96 cases. Moreover, 49 patients were estrogen receptor (ER)- and 65 were ER+. We observed that 22 of 49 ER- and 49 of 65 ER+ subjects showed PD-L1+ expression, respectively.

Conclusion: Our results showed a significant relationship between PD-L1 expression in tumoral cells and TILs, as well as between Ki-67 and TILs. In addition, an inverse correlation was noted between PD-L1 expression and ER. The PD-L1 expression in tumors and TILs and correlation with high Ki-67 may prove the importance of PD-L1 in targeted chemotherapy. An inverse relationship between PD-L1 and ER expression in tumoral cells suggests scope for immunotherapy in ER- IBC. However, further research with more cases is required.