Plasmacytoma

A plasmacytoma is a growth that arises from a single population of plasma cells — the specialised immune cells responsible for producing antibodies. In dogs and cats, these growths occur most often in or just beneath the skin, though they can develop in other locations including the mouth, ears, and digestive tract. They are typically solitary and behave in a benign fashion, but the appearance of any new lump raises questions about what it is and what it may become. Owners often notice a raised, smooth, sometimes ulcerated mass that has appeared over weeks to months, commonly on the head, ears, limbs, or trunk. The growth may be pink, red, or the colour of the surrounding skin, and it may bleed if traumatised. Less commonly, a plasmacytoma may develop in the mouth or along the gastrointestinal tract, where it may be discovered during investigation of other signs. This page explores the signals that bring plasmacytomas to attention, the biological behaviour that distinguishes them from other plasma cell disorders, the ways they are investigated and characterised, and the approaches used to address them. The goal is to orient you to what may be unfolding and what the road ahead typically looks like.