PDCD1 and breast cancer: Further analysis of the relationship between the expression of ten immune checkpoint-related genes and DDIT4 showed that DDIT4 expression was positively correlated with BTLA, CD274, CTLA4, HAVCR2, ICOS, LAG3, PDCD1, PDCD1LG2, TIGIT, and VSIR expression in breast cancer (Fig. 9).