Immunotherapy Combined with Radiation Therapy in Breast Cancer: A Rapidly Evolving Landscape

Immune checkpoint inhibitors (ICI) can have significant anticancer activity, and are approved for many different cancer types, including breast cancer. In breast cancer, programmed cell death 1 (PD-1) inhibitors in combination with chemotherapy have demonstrated significant clinical benefit in early-stage and metastatic settings; however, these combinations can have significant side effects, and there are still many breast cancer patients who do not respond to these approaches. Novel combinations with immunotherapy are needed to improve responses. Given the effects of radiation therapy (RT) on the tumor micro-environment, combinations of RT with immune checkpoint blockade are active areas of investigation. In this review, we discuss experience ICI in breast cancer, including current clinical indications, emerging data in combination with RT, and ongoing studies exploring optimal dosing of RT, and novel combinations with other therapeutics.