Public release date: 18-Nov-2007
St. Louis, Nov. 18, 2007 — A multinational team of researchers has shown for the first time that the immune system can stop the growth of a cancerous tumor without actually killing it.
Scientists have been working for years to use the immune system to eradicate cancers, a technique known as immunotherapy. The new findings prove an alternate to this approach exists: When the cancer can’t be killed with immune attacks, it may be possible to find ways to use the immune system to contain it. The results also may help explain why some tumors seem to suddenly stop growing and go into a lasting period of dormancy.
The study’s authors call the cancer-immune system stalemate equilibrium. During equilibrium, the immune system both decreases the cancer’s drive to replicate and kills some of the cancerous cells, but not quickly enough to eliminate or shrink the tumor.
Scientists first proposed that the immune system might be able to recognize cancer cells as potentially harmful more than a century ago. Under a theory that came to be called cancer immunosurveillance, researchers suggested that if this recognition took place, the immune system would attack tumors with the same weapons it uses to eliminate invading microorganisms. Current immunotherapy efforts use therapeutic agents to increase the chances that the immune system will recognize and attack tumors.
But cancer immunosurveillance has been controversial. The theory had begun to fall out of favor over the years, and in 2001, Schreiber, graduate students Vijay Shankaran and Gavin Dunn, and Lloyd Old, M.D., director of the New York branch of the Ludwig Institute for Cancer Research, proposed a major revision. They called their new model cancer immunoediting.
“We don’t think the immune system has evolved to handle cancers,” Schreiber notes. “Cancer is typically a disease of the elderly, who have moved beyond their reproductive years, so there probably was no evolutionary pressure for the immune system to find a way to fight cancer.”