Here we show that the interaction between PD-1 and PD-L1 increases breast and prostate cancer cell resistance to doxorubicin and docetaxel in vitro and that inhibition of the PD-1/PD-L1 axis using targeted therapy against PD-1 enhances the effect of conventional chemotherapy to attenuate metastasis in an in vivo model of mammary carcinoma. The gene discussed is CD274; the disease is prostate carcinoma.