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What Causes Lumps on the Rear Legs of Cats?

Last Updated on November 7, 2023 by Nicole Cosgrove

Hello, I have a 12-year-old orange tabby who has developed a small bump on his one hind leg. It was pink & looked like a pimple without a head. I checked it today & it is scabby & a bit bigger. I am just wondering if this is something I should worry about. I do plan to bring him to my vet but have never seen this on any cat I have owned before. Any advice would be appreciated.

Thanks for your time.


Based upon your description, the lump most likely is benign. Reactions to fleas, food, or environmental allergens can lead to scabby lumps like the one you describe. Cysts, benign tumors, and small areas of infections also may cause small pimple-like growths anywhere on the body.

However, you caught my attention by mentioning the mass is on a hind leg. Rabies and leukemia vaccines are administered in the rear legs, and these vaccines have been linked in rare instances to aggressive tumors called sarcomas. These so-called vaccine associated sarcomas usually appear as firm masses that develop under the skin. They generally do not cause redness or scabbing of the overlying skin. In other words, the lump on your cat’s leg does not sound like a sarcoma.

However, sarcomas are serious. I always recommend vet checkups for cats with masses in spots where vaccines are administered (the rear legs or in between the shoulders). Your cat is no exception. Your vet should be able to determine whether there is any cause for concern.

About the Author

Dr. Eric Barchas
Dr. Eric Barchas

Dr. Eric Barchas is a professional traveler who spends his spare time working as a full-time veterinarian; contributing to Dogster and Catster; walking, cooking, camping, and exploring the outdoors; skiing (when conditions permit); and reading Booker-shortlisted novels. In between trips Dr. Barchas lives and works in the San Francisco Bay Area with his wife, Denise, and his canine pal, Buster. His main veterinary interests are emergency and critical care, wellness, pain management and promotion of the human-animal bond. Dr. Barchas has to Dogster and Catster since May 2005. 

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