Mast Cell Tumours in Cats

Mast cell tumours are growths that develop from mast cells, a type of immune cell that normally lives in the skin and other tissues. In cats, these tumours most often appear as lumps or nodules in the skin, though they can occasionally develop in internal organs. The behaviour of mast cell tumours in cats tends to differ from that in dogs—many in cats are less aggressive, though patterns vary depending on where the tumour is located and what it looks like under the microscope. Owners typically notice a lump on the skin, often on the head, neck, or body. The lump may have been present for weeks or months, may be growing slowly or quickly, and may be single or multiple. Some cats show no other signs; others may have changes in the skin around the lump, or occasionally signs related to substances released by the mast cells themselves. This page explores what signs may be observed, what is happening at the cellular level, how these tumours are investigated and classified, and what approaches exist for managing them. The goal is to help you understand the landscape of possibilities and the questions that shape decision-making.