Cancer patients often relapse after seemingly successful chemotherapy — perhaps because cellular stress responses to the drugs shield some cancer cells, creating a protected reservoir that can seed fresh tumour growth.
Luke Gilbert and Michael Hemann at the Massachusetts Institute of Technology in Cambridge studied the environment surrounding tumour cells in a mouse model of Burkitt's lymphoma, a cancer of the lymphatic system. They found that normal cells in the thymus, an organ that consists mainly of lymphatic tissue, release two proteins in response to the DNA damage caused by chemotherapy. Those proteins, IL-6 and Timp-1, then protect nearby lymphoma cells from the lethal effects of the drugs.
The same thing happened in human liver-cancer cells grown in culture and treated with doxorubicin, a common treatment for liver cancer.