A protein called Muc4 may be the essential ingredient that allows breast cancer to spread to other organs and resist therapeutic treatment. The study, which appeared in Cancer Research, is one of the first to characterize the role of Muc4 in the disease. Cancer researcher Kermit Carraway said the study indicates that Muc4 may be promoting the release of breast cancer cells from the primary tumor and then inhibiting their death. The finding could lead to new drugs targeting Muc4, which is a central cellular mechanism for metastasis of many cancers.