Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: A plasmacytoma is a tumor of plasma cells, a type of immune cell. In dogs, most are small, smooth skin lumps, often on the lips, gums, ears, toes, or legs, in middle-aged and older dogs. Most skin plasmacytomas behave benignly and are cured with surgical removal. Less commonly, they occur in the intestines or bone, or are linked to multiple myeloma, a more serious cancer, so testing after diagnosis matters.
Signs
- A small, firm, raised, often hairless or red lump
- Common on lips, gums, ears, toes, and legs
- Mouth plasmacytomas may bleed
- Intestinal forms can cause vomiting, diarrhea, or bleeding
Diagnosis
- Fine needle aspirate or biopsy
- Bloodwork, and sometimes protein tests, if multiple myeloma is suspected
- Imaging for non-skin locations
Treatment
- Surgical removal, which is curative for most skin plasmacytomas
- Radiation for tumors that can’t be fully removed
- Chemotherapy for multiple myeloma or widespread disease
Outlook
Excellent for most skin plasmacytomas removed completely. More guarded for intestinal or bone forms or multiple myeloma.
More: fine needle aspirates.
Sources
- Merck Veterinary Manual: Plasma cell tumors in dogs
- Veterinary Cancer Society: See Something, Do Something campaign
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.