In an article published in The Townsend Letter for Doctors, Dr. Anthony Cichoke said that scientific studies show that maitake is the most potent immunostimulant of all the mushrooms. The most medicinally effective way to take maitake is to use the D-fraction, a standardized extract of the active consitituent 1.6 beta-glucan, developed by Hiroki Namba, Ph.D., of Kobe Pharmaceutical University, Kobe, Japan. Dr. Namba discovered that 90% of mice injected with cancer cells and then fed maitake D-fraction did not show any evidence of metastasis of cancer cells. In another study on humans, Dr. Namba reported that "tumor regression or significant symptom improvement was observed in 11 of 15 breast cancer patients, 12 out of 18 lung cancer patients, and 7 of 15 liver cancer patients." Even when tumor regression was not observed, most of the patients taking maitake claimed improvement of overall symptoms one way or another. When maitake D-fraction was administered in conjunction with chemotherapy, the responses improved by 12 percent to as much as 28 percent. Also, the various side effects of chemotherapy, such as hair loss and nausea, were greatly reduced among about 90% of the patients studied. Reduction of pain was also reported from 83% of cancer cases studied.

In the past twenty years medical researchers in several countries have been studying the anti-tumor activity of many types of mushrooms. Most medicinal mushrooms, such as reishi, shiitake, and maitake, show a common property of enhancing immune function by stimulating cell-mediated immunity. Simply put, they can, for example, turn on the immune system's T-cells, which travel the bloodstream seeking and destroying cancer cells.

The chemical structure of maitake's medicinally active polysaccharide compound, beta 1,6 glucan, is different from the beta-glucans found in other medicinal mushrooms. It is recognized by researchers as a very effective agent for stimulating cellular immune responses. Activity of natural killer cells and cytotoxic T-cells is increased up to 3.0 times by oral consumption of maitake. An increase in the production of interleukin-l, which activates T-cell and superoxide anions, which damage tumor cells, has also been demonstrated by the consumption of maitake.

Although most of the human and animal maitake cancer studies have been done in Japan and China, in 1998 the United States Department of Agriculture (USDA) approved an Investigation of New Drug (IND) application to conduct phase II clinical trials using maitake extract on advanced breast and prostrate cancer patients. The study will examine the immune activity effects of maitake extract on tumor size, clinical symptoms, and quality of life.

Although maitake's anti-cancer properties are impressive, it is its anti-HIV effect that has given the mushroom its greatest notoriety. Studies have shown that maitake improves the helper T-cell count of those with HIV. Researchers at the National Cancer Institute (NCI) said that maitake extract is as powerful as the AIDS drug AZT, but without its toxic side effects. In tissue culture studies, D-fraction was found to enhance the activity of other immune cells as well as T-lymphocytes. One study reported that maitake extract prevented HIV infected helper T cells from being destroyed by as much as 96% in tissue culture!