Medicinal mushrooms are considered an unlimited source of polysaccharides (mainly β-glucans) and polysaccharide-protein complexes and possess various immunological and anticancer properties. In addition, their use in integrative medicine leads to a clear reduction of side effects in patients undergoing chemotherapy or radiotherapy. The literature reports a number of beneficial effects of using mushrooms as health supplements in patients affected by high-grade glioma. The effects of medicinal mushrooms on side effects in patients with brain cancer and a case study report are also described in this review.