Most moles harbor mutations that can trigger deadly skin cancer, but many do not ful-fill any cancerous destiny. Researchers at the University of Michigan at Ann Arbor pinpointed a series of mechanisms that prevent cells in a particular type of mole from continuing to divide, despite having various mutations and tumor-promoting oncogenes. The scientists found that the endoplasmic reticulum, the organelle inside cells that folds amino acids into proteins, can sense the presence of oncogenes and stop its protein folding, thereby shutting down the cancerous cell prematurely.

While this mech anism protects against tumor growth, tumor cells could take advantage of this state—not dead but no longer dividing— “to favor survival and resistance to drugs,” researchers note in the October issue of Nature Cell Biology. In other words, the internal mechanisms can both help guard against cancer as well as help promote its growth.