Mushrooms like reishi (Ganoderma lucidum), turkey tail (Trametes versicolor), and lion’s mane (Hericium erinaceus) contain compounds that help the immune system fight cancer. These include beta-glucans and terpenoids that activate natural killer cells and macrophages, slow tumor growth, and may trigger cancer cell death. While most evidence is preclinical, they show promise as low-risk, immune-supportive allies in cancer care.