What Do Cancerous Lumps Look Like on Dogs?

What Is This Growing Bump on My Dogs Leg?

"I’m concerned about this growing bump on my dog's leg. It’s been there for about three weeks or so, maybe a little longer, but it’s been growing, and I’m scared it’s something bad."—Autumn

It May Be a Mast Cell Tumor

Yes, you are right to be concerned. It would really help to know your dog's age, but a lump that looks like that growing on a Weimaraner’s leg is most likely a type of cancer called a mast cell tumor. (About a fifth of all skin tumors are mast cell tumors, and this breed is predisposed to this type of cancer.) It is possible that this is just an infected insect bite or a patch of ringworm, but since mast cell tumors are known as the “great pretenders,” you should have it checked.

Diagnosing This Type of Cancer

This type of tumor is made up of mast cells, which we all have in our blood. In order to diagnose this for sure, your veterinarian will need to draw some of the cells out by fine needle aspirate (FNA) and look at them under the microscope.

Surgery Is a Very Effective Treatment for Mast Cell Tumors

Once the type of tumor has been determined this way, you can discuss how to treat it. The research varies, but about 70 to 85% of mast cell tumors can be cured by surgery alone. (1) If they are not taken care of, or if it is an aggressive type, they can metastasize and will need surgery, radiation, and chemotherapy.

Signs to Watch For

About half of all dogs with mast cell tumors will also have other signs (2), some of them associated with bleeding and some of them with GI problems. They include:

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• Not eating
• Pale gums
• Abdominal pain
• Black or bloody stool
• Bloody vomit

You did not mention any of these, so hopefully, this is just a mild case and can be removed with surgery before it gets too large. If you have also seen any of these signs in the list, however, your dog needs to get this taken care of even sooner.

Diet Makes a Big Difference

Mast cell tumors are a type of cancer that has been shown to respond to a low-carbohydrate keto-type dog food. You should have this seen, but be sure to read this article and do what you can to improve your dog's chances of fighting off this disease.

There is no way this can be definitely diagnosed without an examination and a biopsy, aspiration, or even an impression to see what kind of cells are involved. You should take him to your regular vet to get this looked at and biopsied as soon as possible.

Sources

1. Kim S, Matsuyama A. Canine mast cell tumors: When to worry about aggressive behavior pre-surgically. Can Vet J. 2022 Dec;63(12):1261-1263. PMID: 36467379; PMCID: PMC9648486. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9648486/
2. de Nardi AB, Dos Santos Horta R, Fonseca-Alves CE, de Paiva FN, Linhares LCM, Firmo BF, Ruiz Sueiro FA, de Oliveira KD, Lourenço SV, De Francisco Strefezzi R, Brunner CHM, Rangel MMM, Jark PC, Castro JLC, Ubukata R, Batschinski K, Sobral RA, da Cruz NO, Nishiya AT, Fernandes SC, Dos Santos Cunha SC, Gerardi DG, Challoub GSG, Biondi LR, Laufer-Amorim R, de Oliveira Paes PR, Lavalle GE, Huppes RR, Grandi F, de Carvalho Vasconcellos CH, Dos Anjos DS, Luzo ÂCM, Matera JM, Vozdova M, Dagli MLZ. Diagnosis, Prognosis and Treatment of Canine Cutaneous and Subcutaneous Mast Cell Tumors. Cells. 2022 Feb 10;11(4):618. doi: 10.3390/cells11040618. PMID: 35203268; PMCID: PMC8870669. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8870669/

This article is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from your veterinarian. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2024 Mark dos Anjos, DVM