PD-L1 expression in HNPCC-associated colorectal cancer

PD-L1 immunohistochemistry is predictive for molecular inhibitors of PD-1/PD-L1 immune checkpoint. Therefore, this study evaluated the PD-L1 expression in patients with Hereditary Non-Polyposis Colorectal Cancer (HNPCC). Immunohistochemical expression of PD-L1 in carcinoma cells, stromal macrophages and lymphocytes of 40 HNPCC-patients with colorectal cancer was scored semi-quantitatively. Focal (2 cases) to extensive (2 cases) PD-L1-immunopositivity of carcinoma cells was detected in 4 out of 40 cases (10.0%). Stromal macrophages were immunopositive in 28 out of 40 cases (70.0%). Lymphocytes showed PD-L1 expression in 3 out of 40 cases (7.5%). Simultaneous immunopositivity of stromal macrophages and tumor cells was detected in two MLH1/PMS2-deficient and two MSH2/MSH6-deficient cases. A subset of HNPCC-associated colorectal cancers in this study clearly showed PD-L1 expression of tumor epithelia and immune cells, therefore, the detection of PD-L1 status is useful.