Selenium plays a vital role in many biological processes and has been shown to enhance immunotherapy’s ability for cancer to work better potentially. When we look at selenium, the more active metabolite is methylselenol. Three forms of selenium convert to methylselenol. These are methylselenocysteine (MSC), selenomethionine (SM), and methylselenic acid. Only the first two, MSC and SM, are found in typical selenium supplements. Of those two, MSC is more effective in converting to the most active form. However, cancer may have low enzyme levels that convert MSC into the active form, making it less effective.