A potential new treatment for mast cell cancers reduces the number of mast cells by ‘mutating’ the messenger RNA (mRNA) before it can deliver instructions for manufacturing the gene responsible for cell proliferation. The method, known as frameshifting, changes the pre-mRNA so that the mature mRNA is degraded and any protein produced from its instructions is altered and inert. In a mouse model, frameshifting directed at the c-KIT gene reduced mast cell tumor size and prevented infiltration into other organs.