Suspicious Lump on Your Dog? Here’s When to Tell the Vet.

When it comes to any suspicious lump on your dog, early veterinary intervention gives the best chances of a good outcome.

Suspicious Lump on Your Dog
Different kinds of bumps and suspicious lumps on your dog can suddenly appear, but it doesn’t always mean that they are cancerous. Photo: ashyda

Two dogs were booked yesterday with the same problem, one after the other.

The reason given in the chart? “Client concerned as a lump has got bigger.”

But whereas one dog needed no further action, the other dog faces referral to a specialist. Why? Because one lump was a harmless fatty bump, but the other was a potentially serious tumor.


What these dogs had in common were concerned humans. They had both done the right action in bringing their pet to the veterinarian to investigate suspicious lumps on the dogs.

Found a Suspicious Lump on Your Dog

Most people find a suspicious lump on their dog and immediately think of cancer.

Are all lumps cancer? No!

A lump is a swelling or area of tissue thickening. There are many reasons a dog can get a “suspicious” lump. For example:

  • A cyst: This is a lump filled with fluid that is secreted from the lining of the cyst.
  • An abscess: This is a discrete collection of pus, usually the result of a bite or scratch.
  • Bruising and thickening: This is a result of a knock or blow.
  • Ticks or foreign bodies: A colleague of mine once diagnosed a “tumor” as a boiled sweet stuck in the dog’s fur.

But what if the suspicious lump on your actually is cancer?

Not all lumps are the same.

There’s a spectrum of seriousness that ranges from “nothing to worry about” to potentially life-threatening. But while it’s the latter that sticks in the mind, the former are more common.


Cancers are also divided into:

  • Benign: The lump grows bigger but won’t spread to other parts of the body.
  • Malignant: These aggressive lumps have the potential to spread to the organs.
Warts are generally harmless for dogs. Photo: Amigos3D

When to Worry About a Suspicious Lump on Your Dog

Get any new lump — or any existing lump that changes in some way — checked out.

There are certain signs that can tell you that an urgent visit to the vet is for the best.

These include:

  • Rapid growth: A suspicious lump on your dog that’s growing quickly can cause problems in 2 ways. First, this may be a hint it’s more aggressive, and second, a large lump is more tricky to remove than a small one.
  • Redness: Some more serious lumps on dogs release chemicals that cause tissue reaction and inflammation. If the bump looks sore or bothers the dog, then get it checked out as a matter of urgency.
  • An ailing pet: Again, some tumors release chemical factors that affect general health. If the dog lacks energy, is losing weight, has tummy troubles or is drinking a lot, then let the vet know.

Common Questions About Suspicious Lumps on Dogs

“What if I can lift the lump up in the skin, away from the tissues underneath?”

This is a good sign, since aggressive lumps often invade the deeper tissues.

But — and it’s a big “but” — some more serious lumps on dogs, such as mast cell tumors, can mimic less harmful ones, so even this sign is no guarantee.

“The dog has had the lump for years, and it’s never changed. Should I worry?”

Again, no change is generally considered a good sign because aggressive cancers are just that and will grow quickly.

However, check those lumps and bumps monthly.

  • Take a photo, if necessary, so you have a record.
  • Better still, photograph the lump next to a ruler so you know the exact size.

If the lump starts to grow, becomes red or changes character, then it is a suspicious lump on your dog — and off to the vet it is.

Check your pet’s lumps often for any changes. Photo: winterseitler

How the Vet Knows the Lump Is Suspicious

During the physical exam, vets will check lymph nodes and closely examine the lump.

They may well take the dog’s breed into account, since certain tumors are more common in some breeds than in others.

For example, mast cell tumors can be serious but can also present as fairly harmless looking skin lumps. If a vet sees a young Boston Terrier, Boxer or Golden Retriever who has a skin lump, they’re inclined to do more tests than for other breeds, even if the lump looks innocent.

Fine Needle Aspirate

An easy test to do at the clinic is a fine needle aspirate.

This is where the vet places a needle into the lump and applies suction with a syringe. This collects a few cells from the lump, which can then be smeared onto a microscope slide.


The cytology, or cell types, present on the slide can give the vet valuable clues about the nature of the problem.

The Most Common Lumps and Bumps on Dogs

This isn’t meant as an exhaustive list but as an idea of the types of lumps that are most common in dogs.

  • Warts: The extra skin tags or lumps of skin are usually harmless but may bleed if caught by a brush or collar.
  • Fatty lumps, or lipomas: These are localized fat deposits that are common in older dogs. Again, they are of no significance other than if they grow so large they become a nuisance.
  • Mammary cancer: This is more common in older female dogs who are not spayed.
  • Mast cell tumors: These can range from those lumps where removing them solves the problem to potentially aggressive lumps that can spread. They’re common in younger dogs, and surgical removal is the best option.
  • Sebaceous cysts: Common in older animals, some cysts are filled with a white, almost toothpaste-like secretion. They are of no concern other than being a nuisance.
  • Histiocytomas: Another skin tumor that occurs in young dogs, these ones do eventually subside of their own accord. However, the problem is mast cell tumors can mimic histiocytomas, so removal is the safest option.

These vets provide great information and advice for those who have found suspicious lumps on their dogs:

Final Thoughts on Suspicious Lumps on Dogs

Check your dog regularly for lumps and bumps.

If you find a new lump or an old lump is growing, get them checked by a veterinarian.

Should the lump be something worrisome, early intervention gives the best chances of a good outcome. So don’t go into denial, but keep calm, carry on and get your pet checked by a vet.

vet-cross60pThis pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Sept. 28, 2018.

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