Deep within most tumors lie areas that remain untouched by chemotherapy and radiation. These troublesome spots lack the blood and oxygen needed for traditional therapies to work, but provide the perfect target for a new cancer treatment using bacteria that thrive in oxygen-poor conditions. Now, researchers have shown that injections of a weakened version of one such anaerobic bacteria -- the microbe Clostridium novyi -- can shrink tumors in rats, pet dogs, and a human patient.