Study examined the expression of PD-1, PD-L1, PD-L2, CTLA-4, LAG-3, and TIM-3 in breast cancer patients by flow cytometry and immunohistochemical analysis and showed that ICR expressions were higher in triple-negative and HER-2 positive patients, and expression levels differed significantly even in tumors in the same molecular subgroup [39]. Here, PDCD1 is linked to breast cancer.