In one study, two distinct populations of nucleated, non hematolymphoid, PD-L1-expressing cells were identified; cytokeratin positive (CK+, PD-L1+, CD45−) and cytokeratin negative (CK−, PD-L1+, CD45) cells, both with cytomorphological features consistent of malignant tumor cells [70]. This evidence concerns the gene PTPRC and cancer.