The use of chemotherapy and radiation for cancer treatment can result in cutaneous adverse events (AEs) such as toxic erythema of chemotherapy (TEC) and radiation-induced dermatitis. High-dose vitamin D supplementation has been suggested to potentially improve and shorten recovery for these AEs, primarily based on data from case reports and case series. In this article, we discuss the role of vitamin D in the most prevalent cancers (breast and colorectal cancer) and changes in vitamin D levels after chemotherapy or radiation treatments. We also summarize reports on high-dose vitamin D supplementation for treating chemotherapy-induced and radiation-induced skin toxicity. Larger studies and randomized controlled trials are essential to clarify the roles of vitamin D in malignancy and in cutaneous AEs associated with cancer treatment. The existing studies we reviewed lack standardized dosing regimens and exhibited heterogeneity across study populations, making it challenging to draw generalizable conclusions.