A Ludwig Cancer Research study has uncovered a key mechanism by which tumors develop resistance to radiation therapy and shown how such resistance might be overcome with drugs that are currently under development. The discovery addresses a longstanding challenge: as many as 40% of large tumors develop resistance to radiotherapy, significantly complicating treatment. Overcoming such resistance could go a long way toward treating tumors, especially those that cause significant discomfort to patients and resist other modes of therapy or cannot be surgically removed.