Cat Lipoma: Causes and Treatment Options

Petting cats is a proven stress reducer, and cat parents do it frequently. As our cats age, we may start to feel bumps on the body that make us worry. Perhaps your first thought is cancer. Fortunately, approximately half of lumps in the skin or just under the skin in cats are benign, meaning not cancerous. If you visit your veterinarian, and she diagnoses a lipoma, you shouldn’t worry much. Read on to better understand lipomas, and what they could mean for your cat.

What Are Lipomas in Cats?

Lipomas are benign tumors, meaning they do not spread to other parts of the body (i.e., do not metastasize). While lipomas are very common in dogs, they are not that common in cats. Lipomas are made of adipocytes, also known as fat cells. For this reason, they feel like…well, fat. Lipomas are a little soft and a bit squishy. The difference between general fat and lipomas though is lipomas are fat cells inside of a round capsule. This makes the lipomas discrete from surrounding fat.

There are three types of lipomas in cats to know about:

Simple lipomas. Simple lipomas are small tumors that live in the fat layer found just beneath the skin. They tend to be pretty easy to feel on the outside of your cat. Simple lipomas are usually found on your cat’s trunk (his sides, belly, or back) or on his legs. In some cases, cats can have a lipoma inside the chest or inside the belly.

Myelolipoma. A rare form of lipoma is myelolipoma, which is a tumor of both fat cells and hematopoietic cells, or the cells that form the components of blood similar to what is inside bone marrow. These are benign tumors.

Infiltrative lipoma. In incredibly rare circumstances, cats develop what is known as an infiltrative lipoma. Instead of a round distinct capsule of fat cells, this tumor infiltrates—or invades—tissues around it. These are most commonly located on the thigh (upper muscles of the back leg). Sometimes the leg appears bulky and there is no distinct tumor. The muscles of the thigh feel harder than otherwise expected.

What Causes a Cat Lipoma?

There is no known cause of lipomas. The average age of cats diagnosed with a lipoma is 9.6 years old. Domestic shorthaired cats are the most common breed affected. Siamese cats may be more prone to having lipomas.

If lipomas are tumors of fat cells, it is a natural assumption that being overweight must cause lipomas. At this time, there is no firm evidence to suggest that your cat’s weight is directly linked to his risk of lipomas. Over half of pet cats in the United States are overweight or obese, so it’s no surprise the majority of cats who have lipomas are overweight. However, a 2018 study on lipomas in dogs noted that dogs over average weight were 2 times more likely to have a lipoma (1). More research is needed on this subject.

Lipoma in Cats Symptoms

The majority of cats with lipomas have no symptoms. Some lipomas can become very large and affect movement, but this is uncommon. If a lipoma is present inside the chest, increased effort to breathe, fast breathing rate, decreased activity level, and decreased appetite can occur. If a lipoma is present inside the belly, symptoms may include vomiting and decreased appetite. In rare cases, a myelolipoma of the spleen can rupture causing uncontrolled bleeding. Fast shallow breathing, increased size of the belly, and collapse are symptoms of internal bleeding.

For infiltrative lipomas, a back leg is often affected. As the lipoma grows in between muscles, it often causes changes in the way your cat walks, a change in behavior, i.e., less or no jumping, decreased activity, and limping.

Cat Lipoma Diagnosis

Simple lipomas can be poked with a small needle and the needle contents examined under a microscope. Individual cells are examined in a test called cytology, which reveals fat cells. Sometimes, if a veterinarian is unsure whether the tumor is truly a lipoma, she will recommend a biopsy. After a short surgical procedure under anesthesia, during which a piece (or all) of the tumor is taken, a pathologist will look at the tissue in sections and provide a certain (definitive) diagnosis. For infiltrative lipomas, a surgical biopsy is necessary—a needle cannot diagnose this tumor.

For the uncommon cases involving lipomas inside the chest or abdomen, X-rays are a good place to start to identify the mass and its general location. Ultrasound is an ideal way to better evaluate the density of the mass, and possibly place a needle through your cat’s skin into the mass to get a very small sample. A biopsy can be done especially on tumors in the belly.

Treatment for Lipomas in Cats

Simple lipomas rarely need to be treated. Unless it grows very large and affects how your cat walks, these lipomas are almost always harmless. Pet parents should monitor for sudden increase in size or other changes such as ulceration to the skin (top layer of skin is gone, leaving raw tissue exposed). If this occurs, the tumor should be re-evaluated. While uncommon, a tumor that appears to be just a lipoma can have another type of tumor present.

Lipomas in the chest or belly can be monitored, but if a cat develops symptoms, surgical removal is necessary. Infiltrative lipomas require treatment. Pain medication will help keep your cat comfortable. Surgical removal is ideal but is very difficult, requiring extensive surgery to remove the entirety of the tumor. Chemotherapy and radiation therapy have not been used routinely in the treatment of cat lipomas. 

Cost to Treat Lipomas in Cats

For most lipomas, pet parents will pay for cytology from a needle biopsy, approximately $50-$200, but no treatment is needed. If surgery of the belly is required to remove a tumor, the cost may be anywhere from $1,500 to $5,000, depending on how complex the surgery and care afterward is (such as if internal bleeding occurred). Surgery to remove infiltrative lipomas is approximately the same cost, depending on how large and severe the tumor is.

How to Prevent a Cat Lipoma

There are no known prevention methods for lipomas. While there is no strong evidence that maintaining a healthy body weight will prevent lipomas, there may be a connection. Avoid free-feeding your cat—measure how much he eats every day. Encourage exercise with a variety of toys and actively play with your cat at least twice daily. Ask your veterinarian to assess his weight. If your cat is overweight, your vet can give you advice on how much and what to feed your cat to ensure safe weight loss. 

References

1. O’Neill DG, Corah CH, Church DB, Brodbelt DC, Rutherford L. Lipoma in dogs under primary veterinary care in the UK: prevalence and breed associations. Canine Genet Epidemiol. 2018;5:9. Published 2018 Sep 27. doi:10.1186/s40575-018-0065-9