By Jennifer Coates, DVM
While you’re petting your cat, you feel a bump that wasn’t there before. What is it? Is it serious? Chances are only your veterinarian can tell you, but it helps to know what the most common types of skin lumps on cats are and some tricks you can use to tell them apart.
When a relatively large pocket of pus forms under the skin (or within another tissue) it is called an abscess. Abscesses are localized infections that typically develop after a wound has healed over, which prevents the pus from draining. Puncture wounds, including those that result from bites, are common causes of abscesses in cats. Cats of all ages can develop abscesses, but individuals who go outside or live in multi-cat households where fights occur are at highest risk.
Abscesses are usually painful, cause high fevers, and will sometimes rupture and release foul-smelling pus. Treatment for abscesses can include surgery to drain the pus and thoroughly clean out the affected area as well as antibiotics.
Cysts are hollow structures that are filled with a liquid or other material. Unlike abscesses, cysts are not caused by infection, but they can become secondarily infected. Cats may develop a single skin cyst or multiple ones over a period of time, and they can occur at any time in a cat’s life.
Cysts tend to be round or oval and while they may be firm, you should be able to feel a softer center. Lancing and draining the material from within a cyst will shrink the structure and make it less evident, but with time it usually reforms. Surgery to remove a cyst is the best form of treatment.
Chronic infections and/or inflammation can lead to the formation of a granuloma, a solid mass within the skin that is made out of inflammatory cells, connective tissue, and blood vessels. Cats are at particular risk for developing something called “eosinophilic granuloma complex,” which refers to three different types of skin growths, all of which can be associated with allergies, bacterial infections, and/or genetics:
- An eosinophilic granuloma (also called a linear granuloma) typically develops as a long, narrow lesion running down the back of the thigh or a lump on the lower lip or chin. Sometimes the footpads are involved. The skin is usually pink or tinged yellow, raised and bumpy, and hairless.
- Eosinophilic plagues typically affect the skin of the abdomen, inner thigh, throat, or around the anus. The areas are raised, pink or red, and appear “raw.”
- Indolent ulcers (also called rodent ulcers) affect a cat’s upper lip and sometimes the tongue. These lesions usually look like pink, eroded sores.
Eosinophilic granuloma complex usually responds well to treatment with corticosteroids (e.g., prednisolone) but cats who are severely affected may need other immunosuppressive drugs (e.g., cyclosporine or chlorambucil) or even surgery.
Skin tumors in cats can usually be easily felt once they’ve reached a certain size. They may be either malignant (having the tendency to spread or otherwise significantly worsen) or benign (not having that tendency). Cats with tumors tend to be older, although this is not true for every type of cancer. A biopsy is almost always required to identify the type of tumor that a cat has and to plan what treatment (surgery, chemotherapy, radiotherapy, and/or palliative care) would be in the cat’s best interests.
The following are several of the more common types of tumors that might be felt in or under a cat’s skin:
- Basal Cell Tumors are the most common type of skin tumor in middle-aged to older cats. Thankfully they are benign. These small, firm masses are usually found around a cat’s head and neck. Siamese, Himalayan, and Persian cats are most commonly affected. Surgery to remove a basal cell tumor should eliminate it.
- Squamous Cell Carcinomas often are diagnosed around the ears, nose, and eyelids of older cats. These areas usually have thin fur and less pigment than other parts of the body and so are not well-protected against the cancer-causing effects of sun exposure. Early on, the cancer may simply look like a red patch of skin covered with a scab, but given time it will worsen. Even though squamous cell carcinoma of the skin rarely spreads to distant parts of the body, it can be deadly because it is very invasive. Treatment (e.g., surgery or radiotherapy) is most likely to be successful when it is begun early.
- Mast Cell Tumors can occur alone or as multiple tumors, usually around the head and neck of cats, but sometimes they will also involve the spleen, liver, and/or bone marrow. Mast cell tumors of the skin are usually not very aggressive in cats and surgery to remove them often results in a cure. If a cat’s spleen, liver, or bone marrow is involved, the prognosis is worse.
- Sebaceous adenomas look like a lot like warts. They can occur anywhere on a cat’s body, although the head is a common location. These skin tumors are benign, but if they are bothersome, they can be removed.
- Fibrosarcomas are aggressive cancers. They typically don’t spread to distant parts of the body until late in the disease process, but they are very invasive at their original site. They tend to be firm and grow quickly within or under the skin. Some cats have developed fibrosarcomas at previous injection sites. Treatment usually involves some combination of surgery, radiotherapy, and chemotherapy. Prognosis depends on the size, type, and location of the tumor and how early and aggressively it is treated.
This isn’t an exhaustive list of all the lumps and bumps you might feel on your cat. If you find something new, bring it to your veterinarian’s attention. Sooner is better than later, particularly if the mass is growing or if your cat seems to feel under the weather.