Apoptosis constitutes a strictly programmed device for the removal of aged, damaged and abnormal cells. Research in the last decade has revealed a promising future for apoptosis-based cancer therapies. However, chemotherapeutic agents exhibit an indiscriminate killing that involves both cancer cells and many normal cells. It is therefore of particular interest to find agents that have the ability to induce apoptotic activity specifically in cancer cells and with minimal side effects. Interest in microbe-based approaches to cancer therapy has recently reemerged. The use of S. cerevisiae, the baker’s yeast, as a novel approach for the treatment of cancer is based on the concept that tumor cells undergo apoptosis upon phagocytosis of yeast.

Our data shows that: 1) Heat killed yeast induces apoptosis in multiple human cancers [e.g. breast, tongue and colon] in vitro, 2) yeast has no toxicity against normal cells, 3) induction of apoptosis is yeast-specific, 4) apoptotic activity of yeast in cancer cells is enhanced by MGN-3/biobran (also known as Lentin Plus 1000), a biological response modifier, and importantly, 5) the phenomenon of yeast induced apoptosis was observed in vivo in athymic nude mice model. Electron microscopic studies of tissue samples obtained from in vivo yeast—treated tumors clearly show tumor cells phagocytize yeast and then undergo apoptosis. The molecular mechanism underlying this phenomenon is currently under investigation in our laboratory. Further investigation into this area may present clinical implications for the treatment of cancer.