Why Do Dogs Get Fatty Tumors?

Fatty tumors, or lipomas, are benign growths of fat cells, and no one knows exactly why a particular dog develops one. Large studies do show clear patterns, though. Lipomas are much more common in older dogs, in dogs at or above the average weight for their breed and sex, in neutered dogs, and in certain breeds such as Weimaraners, Dobermann Pinschers, German Pointers, Springer Spaniels, and Labrador Retrievers (O'Neill et al., 2018).

Lipomas are common. In a study of more than 384,000 dogs in UK primary care practices, about 1 in 50 had a lipoma recorded in a single year (O'Neill et al., 2018). Most cause no harm. In a follow-up study of the same dogs, lipomas contributed to only 1.8% of deaths among dogs with lipomas (Pegram et al., 2020).

Still, a fatty-feeling lump isn't always a lipoma. Some fatty tumors grow into muscle, and a few are cancerous liposarcomas (Liptak, 2017), so every new lump deserves a check.

Key points

• About 1.94% of dogs had a lipoma recorded in one year, roughly 1 in 50 (O'Neill et al., 2018).
• Dogs aged 9 to under 12 had 17.52 times the odds of lipoma compared with dogs aged 3 to under 6 (O'Neill et al., 2018).
• Dogs at or above their breed and sex average weight had nearly twice the odds of lipoma (O'Neill et al., 2018).
• Neutered males and neutered females had higher odds than intact females (O'Neill et al., 2018).
• Weimaraners had the highest breed prevalence, at 7.84% (O'Neill et al., 2018).
• These are associations, not proven causes. The link with weight, for example, still needs confirmation (O'Neill et al., 2018).

Detailed explanation

What a fatty tumor is

A lipoma, also called a fatty mass or fatty lump, is a benign growth of fat tissue (O'Neill et al., 2018). Lipomas are very common in dogs (Liptak, 2017). Only testing, such as a needle sample, can confirm one (Liptak, 2017). Our article on lumps that aren't cancer compares lipomas with other benign growths, and bumps on dogs covers the wider range.

Age

Age is the strongest pattern. In the UK study, dogs aged 9 to under 12 had 17.52 times the odds of having a lipoma compared with dogs aged 3 to under 6 (O'Neill et al., 2018). That's why fatty lumps are often thought of as a senior dog problem, and why new lumps on an older dog are so common.

Body weight

Weight matters too. Dogs at or above the average adult weight for their breed and sex had 1.96 times the odds of lipoma compared with lighter dogs, and the odds rose as weight increased (O'Neill et al., 2018). The researchers noted a strong association between obesity and lipomas and suggested weight control as a reason to keep dogs lean, though they said the link needs further study to confirm (O'Neill et al., 2018; Royal Veterinary College, 2018).

There's also early laboratory work on how fat tissue and lipomas might be connected. One study found that overweight dogs had significantly higher activity of a growth-related gene called HMGA2 in the fat under their skin. The authors proposed that in some lipomas, this gene is permanently switched on, mimicking the growth signal that normally happens when fat tissue expands (Thies et al., 2014). This research is preliminary and doesn't show that weight gain causes lipomas.

Neutering

Neutered dogs were more likely to have lipomas. Compared with intact females, neutered males had 1.99 times the odds and neutered females had 1.62 times the odds (O'Neill et al., 2018). This is an association, and the study doesn't show that neutering causes lipomas.

Breed

Some breeds are clearly more prone. The breeds with the highest one-year prevalence in the UK study were (O'Neill et al., 2018):

• Weimaraner, 7.84%
• Dobermann Pinscher, 6.96%
• German Pointer, 5.23%
• Springer Spaniel, 5.19%
• Labrador Retriever, 5.15%

Purebred dogs overall had slightly higher odds than crossbreds (Royal Veterinary College, 2018). A breed link suggests genetics may play a role, though this research didn't identify specific genes. If you have a Lab, our article on cancer in Labrador dogs covers that breed's other lump risks.

Insured dogs

Insured dogs had 1.78 times the odds of lipoma (O'Neill et al., 2018).

How lipomas are diagnosed and managed

A fine-needle aspirate can confirm a lipoma (Liptak, 2017). In the follow-up UK study, 40.5% of lipomas were diagnosed with a needle sample and 7.8% with a biopsy. Monitoring was recommended for 54.0% of dogs, and 19.0% had surgery (Pegram et al., 2020). Lipomas affected walking in 1.4% of cases and caused suspected pain or discomfort in 0.5% (Pegram et al., 2020). Our articles on fine-needle aspirates and whether they hurt explain the test.

When surgery was done, complications included fluid buildup under the incision (seroma) in 7.8%, wound breakdown in 2.7%, and wound infection in 2.1% (Pegram et al., 2020). Our guide to recovery after cancer surgery covers aftercare that applies to lump removal too.

When a fatty lump isn't a simple lipoma

Not all fatty tumors are harmless. Infiltrative lipomas are benign but grow into nearby muscle and connective tissue, often in the jaw or the chest and belly walls, and they need more extensive surgery (Liptak, 2017). A needle sample can diagnose a lipoma but can't tell a regular lipoma from an infiltrative one, so a biopsy or CT may be needed when a more aggressive tumor is suspected (Liptak, 2017). Rarely, a fatty tumor is a cancer called liposarcoma. Our article on canine liposarcoma explains the difference.

Other lumps need checking too, from harmless sebaceous cysts to mast cell tumors. A lump that's hard and doesn't move needs a prompt look. Our 10-minute dog cancer check can help you track lumps at home.

When to contact a veterinarian

Book an appointment soon if your dog has:

• Any new lump, even if it feels soft and fatty
• A lump that's growing or changing
• A lump that feels firm or fixed in place
• A lump that seems to bother your dog or affect how it walks

Call the same day if a lump is bleeding, ulcerated, or suddenly swollen and painful.

Questions to ask your veterinarian

• Can we do a needle sample to confirm this is a lipoma?
• Could it be an infiltrative lipoma or something else?
• Should we monitor it or remove it?
• Is my dog's weight something we should work on?
• How should I measure and track this lump at home?
• What changes would mean we should recheck it sooner?

Sources

Liptak, J. M. (2017, March 6). Lipoma. Animal Cancer Surgeon. Retrieved November 10, 2026, from https://animalcancersurgeon.com/skin-tumors-lipoma

O'Neill, D. G., Corah, C. H., Church, D. B., Brodbelt, D. C., & Rutherford, L. (2018). Lipoma in dogs under primary veterinary care in the UK: Prevalence and breed associations. Canine Genetics and Epidemiology, 5, Article 9. 

Pegram, C. L., Rutherford, L., Corah, C., Church, D. B., Brodbelt, D. C., & O'Neill, D. G. (2020). Clinical management of lipomas in dogs under primary care in the UK. Veterinary Record, 187(10), e83. 

Royal Veterinary College. (2018, October 10). UK dogs and their fatty lumps: Finally the risks explained. VetCompass. https://www.rvc.ac.uk/vetcompass/news/uk-dogs-and-their-fatty-lumps-finally-the-risks-explained

Thies, H. W., Nolte, I., Wenk, H., Mertens, F., Bullerdiek, J., & Markowski, D. N. (2014). Permanent activation of HMGA2 in lipomas mimics its temporal physiological activation linked to the gain of adipose tissue. Obesity, 22(1), 141-150.