Alternative cancer treatment with nutritional/dietary supplements containing a wide variety of herbal products is on the rise in Western countries. Recent epidemiological studies have suggested that mushrooms may prevent against different types of cancers. <i>Phellinus linteus</i> is a well-known Oriental medicinal fungus with a variety of biological activities, including immunomodulatory or direct antitumor activities. The activity of <i>P. linteus</i> and its extracts is associated with the presence of polysaccharides, their peptide/protein complexes and other low molecular weight complexes. Polysaccharide fractions isolated from P. linteus were found to be related to the increased activity of immune cells such as the production of cytokines by macrophages and B-cells or the increased cytotoxic activity of natural killer cells. Moreover, P. linteus was found to modulate the expression or activity of various genes involved in cell proliferation, apoptosis, angiogenesis, invasive behavior and chemoprevention. Finally, P. linteus extracts demonstrated tumor regression in three independent case reports, suggesting that an extract from P. linteus or a dietary supplement based on the extract from P. linteus may have potential use for the alternative treatment of cancer.