William Coley, a surgeon turned detective used the power of observation to first see the benefits of utilizing one’s own immune system to fight off cancer cells. Truly astonishing since the immune system was not even a known entity. In 1891 Coley started experimenting with bacterial infections and their role in treating advanced cancers commonly sarcomas. Listen to the npr story below for details on his work and what has followed.
http://www.npr.org/sections/health-shots/2015/12/28/459218765/cutting-edge-cancer-treatment-has-its-roots-in-19th-century-medicine