Immune checkpoint inhibitors in malignancies with mismatch repair deficiency: a review of the state of the current knowledge.

The use of immune checkpoint inhibitors to treat malignant tumors with microsatellite instability is an emerging new modality. This is based on the observations that these tumors may have a high mutation rate-thus a potential source of tumor-specific neoantigens-and harbor infiltrating cytotoxic T cells in response, suggesting that they may be particularly susceptible to immune checkpoint therapy. PUBMED and ASCO library were systematically reviewed to identify all relevant data that involved the use of immune checkpoint inhibitors in the treatment of cancers with microsatellite instability. The manual search retrieved a total of 3 relevant articles and 1 abstract published between 2015 and 2016. A total of 61 patients with colorectal, 3 with ampullary/cholangiocarcinoma, 2 with endometrial carcinomas, 3 with small bowel cancers, 2 with glioblastoma multiforme, and 1 with bladder cancer with reported efficacy results were reviewed. All the patients had stage IV cancer and were treated with immune checkpoint inhibitors until progression of disease or intolerable side effects emerged. The range of objective response rate was 25-71%. Responses were also durable with progression-free survival at 20 weeks of around 67-78% and to 46% at 1 year. The use of immune checkpoint inhibitors is effective in cancers that express microsatellite instability.