PDCD1 and breast carcinoma: The differences in cytokine levels between the groups in our study may be attributed to the development of and change in immune responses during the breast cancer course and chemotherapy treatment, and may also be explained by the theory of immunosuppression, which states that breast cancer cells reduce immune function to escape cytotoxicity from immune cells through the programmed cell death protein 1 (PD-1) pathway [29, 30].