Immune Checkpoint Blockade Therapy for Breast Cancer: Lessons from Epithelial–Mesenchymal Transition

Immune checkpoint blockade therapies have generated efficacious responses in certain tumor types; however, the responses of breast carcinomas have been largely limited. Moreover, the identity of various parameters that can predict responses to immunotherapies, and at the same time, serve as putative biomarkers that can be therapeutically targeted to enhance the effectiveness of immunotherapies for breast cancers, remains to be comprehensively delineated. Activation of epithelial–mesenchymal plasticity in cancer cells, including those of the breast, increases their tumor-initiating potential and promotes their aggressiveness and resistance to multiple treatment regimens. Moreover, the residence of cancer cells in alternating epithelial or mesenchymal plastic phenotypic states can also influence their immuno-modulatory properties and susceptibilities to immune checkpoint blockade therapies. In this current opinion, we discuss the lessons that can be learnt from epithelial–mesenchymal transition to potentiate the efficacy of immunotherapy for breast cancers. We also discuss strategies to sensitize more-mesenchymal cancer cells to anti-tumor immunity and immune checkpoint blockade therapies, with the hope that these can serve as new translational avenues for the treatment of human breast tumors.