Checkpoint inhibitor therapy for breast cancer, colon cancer, merkel cell carcinoma and sarcoma

Two of the most common cancers, breast and bowel cancer, seem 'immune' to immune therapy-but there are particular molecular subtypes of these cancers that are more responsive. Several types of cancer that occur rarely or uncommonly may also benefit from immune therapy. The rare cancers suffer from under-representation in phase 3 randomised controlled trials, as conducting such large scale studies in the setting of rare cancers is usually not feasible. This in turn affects regulatory approval and access to checkpoint inhibitors for these tumours. Nevertheless, reported activity of these drugs has led oncologists and patients to consider such therapy, particularly where no other active or effective therapy exists. This review article will review the evidence that supports immune therapy for such cancers.