Dogs and Lipomas: Should You Be Concerned About Fatty Tumors?

Are all fatty tumors benign and what causes them?
By Nancy Kay DVM, June 2014, Updated August 2020
lipomas on dog

Of all the benign growths dogs develop as they age, lipomas, aka fatty tumors are one of the most common. Given the opportunity to examine an older dog, I’ll very likely find at least one or two cutaneous (within the skin) or subcutaneous (just beneath the skin surface) lumps and bumps. Such growths are common by-products of the aging process. In this regard, I liken them to the brown spots that appear on our skin as we get older.

The good news is that most cutaneous and subcutaneous canine tumors are benign. It’s that small population of malignant (cancerous) masses that keeps us on our toes. They are the reason it’s important to have your veterinarian inspect any newly discovered lumps and bumps your dog develops. Lipomas often cause severe anxiety to dog owners when there are multiple or very large masses present on their dogs. So, it’s best to familiarize yourself with what your dog’s healthy normal body looks like by performing regular at-home physical examinations of your dog’s health. The smaller a cancerous growth is at the time of treatment, in general, the better the outcome.

What are Lipomas?

Lipomas are very common fat-based masses (tumor) seen on middle-age and senior dogs that are generally benign. They arise from fat (lipid) cells and they are typically found in the subcutaneous tissue (just beneath the skin surface) of axillary regions (armpits) and alongside the chest and abdomen.

Occasionally lipomas develop internally within the chest or abdominal cavity. Rarely does a dog develop only one lipoma. They tend to grow in multiples and I’ve examined individual dogs with more lipomas than I could count. Fatty tumors that grow between the muscles are called infiltrative lipomas and when malignant (cancerous) they are called infiltrative liposarcomas.

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Can lipomas in dogs grow fast? While generally lipomas are characterized by their slow-growing nature, each one is different and some lipomas have been known to grow quickly.

Should lipomas be treated?

In the vast majority of cases, the answer is a definite, "No!” Lipomas are generally not treated, because of their benign, slow-growing nature. The only issue most lipomas create is purely cosmetic, which the dog could care less about. It should be noted that lipomas do not go away on their own. Lipomas should be examined by a veterinarian to ensure they are benign.

If you suspect your dog has a lipoma, seek out veterinarian assistance on diagnosing the tumor type by fine needle aspiration. This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian.

When to Seek Veterinary Care

There are a few exceptions to the general recommendation to let sleeping lipomas lie. A fatty tumor is deserving of more attention in the following situations:

1. The location of a lipoma may interfere with mobility. If a lipoma is steadily growing in an area where it could ultimately cause problems with a dog's mobility, it might be best to remove it before too large. The armpit is the classic spot where this happens. The emphasis here is on the phrase, “steadily growing.” Even in one of these critical areas there is no reason to surgically remove a lipoma that remains quiescent with no discernible growth.

2. Sudden growth and/or change in appearance of a fatty tumor (or any mass for that matter) warrant reassessment by a veterinarian to determine the best course of action.

3. Infiltrative liposarcoma vs lipoma. Every once in a great while, a fatty tumor turns out to be an infiltrative liposarcoma rather than a lipoma. These are the malignant black sheep of the fatty tumor family. Your veterinarian will be suspicious of an infiltrative liposarcoma if the fine needle aspirate cytology reveals fat cells, yet the tumor feels fixed to underlying tissues. (Lipomas are normally freely moveable.) Liposarcomas should be aggressively surgically removed and/or treated with radiation therapy.

4. Occasionally a lipoma grows to truly mammoth proportions. If ever you’ve looked at a dog and thought, “Wow, there’s a dog attached to that tumor!” chances are you were looking at a lipoma. Such massive tumors have the potential to cause the dog discomfort. They can also outgrow their blood supply, resulting in possible infection and drainage from the mass. The key is to catch on to the mass’s rapid growth so as to surgically remove it before it becomes enormous in size and far more difficult to remove.

Can canine lipomas be prevented?

No one knows because risk factors include a complicated mix of environment, genetics, diet, and care. Anecdotally speaking, it is thought that overweight dogs are more predisposed to developing fatty tumors. While I’m not so sure I buy this, I’m certainly in favor of keeping your dog at a healthy body weight.

Photo by Christiana T

Nancy Kay, DVM, Dipl., American College of Veterinary Internal Medicine, is a 2009 recipient of AAHA's Animal Welfare and Humane Ethics Award and author of Speaking for Spot.