I have been studying medicinal mushrooms for the last 15 years and have reported that of all mushrooms studied, Maitake Mushroom (Grifolafrondosa) has the strongest activity in tumor growth inhibition both in administered orally and intraperi-toneally. In this report, Maitake extract D-fraction was investigated to determine its effectiveness not only on the inhibition against tumors already growing, but also on the inhibition of formation of the secondary focus due to metastasis of tumor cells in lymph and/or blood. In the tests of cancer inhibition rates on mice bearing MM46 (breast cancer), they were bred for one month with food: "Obtaining 20% edible mushroom powder. The result was that Maitake outperformed all other mushrooms. Through the 31 day oral administration, total remission of the tumor was visibly confirmed on four out of ten Maitake fed mice. The remaining six rodents also indicated almost 90% suppression rate compared to untreated (control) mice. Most other mushroom extracts are reported ineffective when given orally. The results of human studies on Maitake D-fraction is reported ivhich indicated strong potential of Maitake D-fraction for cancer treatment.