After receiving chemotherapy, many cancer patients go into a remission that can last months or years. But in some of those cases, tumors eventually grow back, and when they do, they are frequently resistant to the drugs that initially worked.

Now, in a study of mice with lymphoma, MIT biologists have discovered that a small number of cancer cells escape chemotherapy by hiding out in the thymus, an organ where immune cells mature. Within the thymus, the cancer cells are bathed in growth factors that protect them from the drugs’ effects. Those cells are likely the source of relapsed tumors, said Michael Hemann, MIT assistant professor of biology, who led the study.

via Cancer’s hiding spots revealed.