Lack of cytoplasmic expression of a new marker programmed cell death ligand-1 in tumor cells is significant.

BACKGROUND: Recent studies have indicated that an antibody against programmed cell death protein 1-ligand 1 (PDCD1-LG1), a new marker of programmed cell death-ligand 1 expression, is promising for studying the mechanisms of breast cancer (BC) progression and resistance to chemotherapy. AIM: To compare the features of PDCD1-LG1 expression in chemoresistant luminal A BC and BC with high Ki67 indices. METHODS: This prospective single-center observational cohort study included 148 patients with newly diagnosed primary resectable BC. The tumor sections were stained with antibodies against PDCD1-LG1. The statistical calculations were performed using Statistica software version 12.0. P < 0.05 was considered statistically significant. RESULTS: Cytoplasmic PDCD1-LG1 (cPDCD1-LG1) expression was detected in the nonneoplastic epithelium, tumor cells (TCs) and immune cells (ICs). A lack of cPDCD1-LG1 expression in ≥ 20% of TCs and a PDCD1-LG1+ IC score ≥ 10% were associated with aggressive BC characteristics, including tumor G3, estrogen receptor-negative status, overexpression of human epidermal growth factor receptor 2 (HER2+), luminal B HER2+ BC, nonluminal HER2+ BC and triple-negative BC. The lack of cPDCD1-LG1 expression in < 20% of the TCs, in combination with a PDCD1-LG1+ IC score < 10% and G1, was characteristic of chemoresistant luminal A BC, whereas the lack of cPDCD1-LG1 expression in ≥ 20% of the TCs, combined with a PDCD1-LG1+ IC score ≥ 10%, was a predictor of high BC sensitivity to chemotherapy. CONCLUSION: These results indicate that both the lack of cPDCD1 LG1 in TCs and the PDCD1 LG1 IC score and their combination may be important for assessing BC prognosis and sensitivity to chemotherapy.