What Causes Fatty Tumors in Dogs? Are They a Sign of Cancer?

What are fatty tumors (lipomas) in dogs?

Lipomas are growths of fat cells in the fatty tissue layer under the dog’s skin. Most feel soft, rounded, and a little “slippery” under your fingers. They’re typically slow-growing and painless.

You’ll most often find them on the pet’s abdomen, chest, or flanks, but they can appear anywhere on the dog’s body.

How they look and feel (so you know what you’re feeling)

A classic lipoma is:

• Soft or doughy, and it moves a bit over the muscle when you slide it.

• Not ulcerated, not inflamed, and not tender.

• Stable in size for weeks to months, or grows gradually.

That said, not all lumps read the rulebook. Some lipomas can feel firmer, sit between muscle layers, or be located in awkward spots like the armpit, where they rub and bother a dog.

What causes fatty tumors in dogs?

If you’re wondering what causes fatty tumors in dogs, the exact cause isn’t fully known. We do see patterns: age, genetics, and body condition seem to matter. Many lipomas show up in middle-aged and older dogs, and overweight dogs are more likely to develop them.

Some pups form multiple lipomas over time—think of them as “lump-prone” individuals. That doesn’t automatically mean cancer; it means you’ll want a simple plan to check and track each new bump.

Risk factors you can (and can’t) control

• Age: lipomas are common in senior dogs.

• Breed tendencies: Labrador Retrievers, Cocker Spaniels, and some bully breeds seem over-represented.

• Weight: extra body fat correlates with developing lipomas.

• Location/type: rare infiltrative lipomas spread through surrounding tissues and muscle layers rather than sitting loosely under the skin.

Weight and the general pet’s health habits are in your control. Genetics and age aren’t—so early checks matter.

Lipoma vs. cancerous lump: the big difference

A benign lipoma grows from fat and tends to sit quietly. A malignant tumor (for example, liposarcoma or mast cell tumors) can grow rapidly, feel firmly stuck to deeper structures, or ulcerate.

Here’s the key: you can’t tell by sight alone. Two lumps that look identical can be completely different under the microscope.

Red flags that a lump needs attention now

• Growth that doubles in size over weeks

• A mass that’s fixed and won’t slide under the skin

• Ulcerated, bleeding, or painful surface

• Lumps near the groin/axilla that rub and affect walking

• A lump plus whole-body signs: weight loss, low energy, vomiting
  
  

These don’t guarantee cancer—but they do guarantee a vet exam.

Diagnosing lumps and bumps on your dog

Your veterinarian will start with the hands and eyes, then confirm with a quick sampling:

Fine-needle aspiration (FNA). A tiny needle gathers cells (a fine needle aspirate). Many dog lipomas can be identified this way in minutes. It’s quick and usually doesn’t require sedation.

Biopsy & pathology. If FNA is unclear—or the lump is unusual—your vet may recommend removing a small piece or the entire mass. A veterinary pathologist reviews it to deliver an accurate diagnosis, tumor grade, and margin status.

Staging (when indicated). For suspicious masses, your vet might check nearby lymph nodes or take imaging to see if anything has spread to other organs.

Special cases: infiltrative lipomas and liposarcomas

Infiltrative lipomas are still made of fat cells but grow into nearby tissues and muscle layers, making complete removal tougher. Liposarcomas are rare malignant tumors arising from fatty tissue; they behave more like cancer, not a simple lipoma.

Both require careful planning and sometimes advanced imaging or radiation therapy after surgical removal.

Treatment and management of fatty tumors

Most simple lipomas don’t need treatment. Your vet may suggest watchful waiting with measurements and photos.

When we recommend surgical removal

• The lump interferes with walking or comfort

• It’s in a spot that rubs or repeatedly gets irritated

• It’s growing quickly or the diagnosis is uncertain

• You prefer removal after discussing pros and cons

For many dogs, removal is a straightforward day procedure. Your vet will discuss anesthesia, recovery, and any drug interactions or special concerns based on your pet’s condition.

What if surgery isn’t ideal?

Large or awkwardly placed lipomas may be monitored if they’re not causing trouble. Weight management can help slow lipoma growth in some dogs. In rare cases, infiltrative lipomas benefit from radiation therapy after debulking surgery to control regrowth. Your team will tailor the plan.

At-home checks: a simple monthly routine

Once a month, run your hands slowly over your dog, nose to tail. Check the chest, armpits, belly, groin, and thighs. Note new lumps, and measure existing ones with a soft tape. Snap a quick photo with a coin for scale. This is the easiest way to spot changes early.

If a lump changes, schedule a recheck; bring your notes and photos.

When to see a veterinarian

Err on the side of early. Book a visit for any new lump, any change in size/feel/behavior, a lump that bothers your dog, or if you’re simply unsure. Small samples now beat big surgeries later.

Prevention: what you can control

You can’t prevent every lipoma, but you can support your dog’s health:

• Keep your dog at a healthy weight with portion control and daily activity.

• Ask before giving human meds; some can upset skin or stomach.

• Keep routine wellness exams so small issues are caught early.

These habits won’t guarantee a lump-free life, but they stack the odds in your favor.

Where Oncotect fits in proactive care

Lipomas are diagnosed by sampling the dog’s skin—nothing replaces that. But if you’re building a proactive plan, consider pairing regular exams with screening. The Oncotect Cancer Screening Test Kit is a non-invasive urine screen that helps you and your vet spot concerning cancer-associated changes earlier. It doesn’t diagnose skin lumps, yet it can nudge earlier conversations—especially for older dogs or breeds that seem to grow “mystery bumps.”

Explore: Oncotect At-Home Wellness Screen for Cancer

Key takeaways

• Lipomas are common and usually harmless, but testing is the only way to know.

• Watch for rapid growth, ulceration, pain, or fixed/firm lumps—those need faster attention.

• Fine-needle aspiration and, when needed, biopsy provide an accurate diagnosis.

• Many lipomas can be safely monitored; others benefit from surgical removal.

• Keep a simple home check routine, maintain a healthy weight, and partner with your vet.

• Proactive screening—like Oncotect’s at-home test—helps keep you a step ahead on overall cancer risk.
  
  

Final word

If you’re asking what causes fatty tumors in dogs, think age, genetics, and body condition. Most are simple fatty tumors that never threaten your dog’s life. Your job is to notice new bumps, get them sampled, and choose monitoring or removal with your vet’s guidance. Early, simple steps today prevent complicated decisions tomorrow.