For the first time in history, a new path to cancer prevention for those over 40 years of age is disclosed. The common denominator and other bioactive compounds of three different medicinal mushrooms from Japan, China and the Himalayas respected for two millennia have been discovered and Western research into them is presented. They re-arm the immune system which deteriorates as we age preventing some cancers from escaping as they usually do. They also act as a benign chemotherapy without any of the usual side effects killing cancers as they develop. Used in combination with traditional methods of cancer treatment,there is a dramatic drop in side effects of chemotherapy and radiotherapy with increased and prolonged remissions that demand immediate methodologically sound research.Just one bioactive compound has taken up 25% of Japanese Government spending on all anti-cancer agents for over 30 years. We must all re-arm our immune systems now and consider preemptive use.