Combining Radiation Therapy with Immune Checkpoint Blockadein Breast Cancer

Purpose of Review Immune checkpoint blockade (ICB) is an emerging therapy in breast cancer. Its optimal integration with radiation therapy (RT) for breast cancer remains to be established. Herein, we review the current evidence on combining ICB and RT in breast cancer and discuss the challenges, open questions, ongoing trials, and future directions for use of this treatment combination. Recent Findings Early trials of ICB in breast cancer show evidence of a modest response, limited due to the low baseline immunogenicity of most breast cancers. RT, as a potent stimulator of the immune system, has been used in combination with ICB with encouraging results. The optimal dose, fractionation, and timing of RT combined with ICB are active areas of investigation. Preclinical evidence suggests that moderate-dose, hypofractionated courses may be more effective at stimulating an immune response than high-dose, single-fraction courses. Recent studies suggest that ICB can be active in breast cancer, but optimizing the response rate remains a challenge. The immunostimulatory effects of RT have the potential to overcome this obstacle, with promising data from preclinical and early clinical trials. Future investigation on the optimal dosing and fractionation of RT in combination with ICB will be critical.