Emerging therapies for rare cutaneous cancers: A systematic review

Background: Rare cutaneous cancers require early management given their aggressive nature; however, few therapeutic options exist for managing these rare cancers. Objective: To identify emerging therapies for extramammary Paget's disease, Merkel cell carcinoma, sebaceous gland carcinoma, microcystic adnexal carcinoma, Kaposi sarcoma and cutaneous angiosarcoma. Methods: A systematic review was conducted using PubMed database from October 2010 to October 2020. Published clinical trials and case reports/series were included if they involved primarily a targeted agent rather than classic cytotoxic chemotherapy or photosensitizing medication. Active clinical trials were evaluated using ClinicalTrials.gov, the Japanese University Hospitals Clinical Information Network, and the ISRCTN registry. Quality of evidence for each study was rated using the Oxford Centre for Evidence-Based Medicine Level of Evidence Rating Scale. Results: There are several emerging therapies for rare cutaneous cancers with many clinical trials actively recruiting. PD-1 receptor inhibitors were the most investigated treatment, targeting several cancers. Merkel cell carcinoma and Kaposi sarcoma had the most clinical trials while microcystic adnexal carcinoma and sebaceous gland carcinoma had the least. The main limitation was a lack of key findings from clinical trials still in progress. Conclusions: Emerging therapies exist for rare cutaneous cancers; results of ongoing studies will provide more robust evidence in the future.