Cancer patients tend to have reduced serum selenium concentrations compared to healthy controls. Adjuvant selenium supplementation improves the protection of healthy tissue in tumor patients undergoing radiation therapy [Muecke 2018].
In a 2018 review of 15-years of experience with selenium supplementation in radiation oncology, Muecke et al  reported on two randomized controlled trials. The researchers observed positive effects of the supplemental selenium and no adverse effects in the patients undergoing radiation therapy:
- 81 patients with uterine cancer
- 39 patients with head and neck tumors
Selenium Deficit in Cancer Patients
In the majority of the tumor patients (carcinomas of the uterus, head and neck, lungs, rectum or prostate) whom they examined, German researchers found a relative selenium deficit in whole blood or serum [Muecke 2018].