Skin Lumps or Bumps in Cats

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During the course of grooming, playing with or handling your cat, you may discover a lump or bump or or beneath the skin. To learn what it may be, see this table on lumps or bumps on or beneath the skin.

• Abscess: A painful collection of pus at the site of a bite or puncture wound. Frequently found after cat fights. Forms a firm swelling that becomes soft with time. Purulent discharge.
• Cancer: A lump that indicates cancer is characterized by rapid enlargement; appears hard or fixed to surrounding tissue; any lump growing from bone; a lump that starts to bleed; a mole that begins to spread or ulcerate; an unexplained open sore that does not heal, especially on the feet or legs. The only way to tell for sure is to remove and study the lump under a microscope. Better to check out a benign lump than to miss a malignant one.
• Epidermal inclusion cyst: A firm, smooth lump beneath the skin. May grow slowly. May discharge cheesy material and become infected. Otherwise, not painful.
• Grubs/Cuterebra: Inch-long fly larvae that form cystlike lumps beneath the skin with a hole in the center for the insect to breathe. Often found beneath the chin, on the neck, or along the abdomen.
• Hematoma: A collection of clotted blood beneath the skin; often involves the ears. Caused by trauma. May be painful.
• Mycetoma: Mass or nodule beneath the skin with an open tract to the surface draining a granular material. Caused by a fungus.
• Skin papilloma: These grow out from the skin and may look like a wart or a piece of chewing gum stuck to the skin. Not painful or dangerous.
• Sporotrichosis: Skin nodule with overlying hair loss and wet surface of pus at the site of a puncture wound or break in the skin. Caused by a fungus.

Any sort of lump, bump, or growth found on or beneath the skin is, by definition, a tumor, which literally means a swelling. Tumors are classified as benign when they are not cancer, and malignant when they are.

Classically, a benign growth is one that grows slowly, is surrounded by a capsule, is not invasive, and does not spread. However, there is no reliable way to tell if a tumor is benign or malignant without removing it and examining it with a microscope. If the tumor is benign, it won't come back if it is completely removed.

Cancers usually enlarge rapidly (a few weeks or months). They are not encapsulated. They appear to infiltrate into surrounding tissue and may ulcerate the skin and bleed. A hard mass that appears to be attached to bone or could be a growth of the bone itself is a cause for concern. The same is true for pigmented lumps or flat moles that start to enlarge, then spread out and begin to bleed (melanomas).

A hard gray or pink open sore that does not heal, especially on the feet and legs, should be regarded with suspicion. This could be a skin cancer.

Any unexplained nodules, bumps, or open sores on your cat should be checked by your veterinarian. Most cancers are not painful. Do not delay simply because your cat does not seem to be feeling uncomfortable.

This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.