No-one wants to find a lump on their dog, but worse still is not finding that lump. Like a bad smell, the longer a growth goes undetected, the worse it can get. But once aware of the lump you can seek help and take back control.

Don’t Panic but Do Act

Don’t panic, but also don’t ignore the lump. The vet is your best resource for finding out what’s what. But whilst waiting for the appointment, here is some common sense information about lumps.

The thing with a skin growth on a dog is it can be difficult to tell worrying tumors from less troublesome cysts, warts, or fatty lumps. That’s because it’s what’s matters happens inside on a cell level. Think of this like two cans of food with the labels removed. Looking from the outside it’s impossible to know what’s inside.  It’s only once the can is opened you discover one is baked beans and the other is dog food.

The vet equivalent of opening the can is to take a small amount of tissue from the lump and send it for analysis. Happily, this may not be necessary for every single lump, because to the trained eye some lumps are less worrying than others. The vet will use their judgement to advise a course of action.

More of the diagnostics later…first let’s consider what’s worrying and what’s not when it comes to lumps.

Warning Signs to Watch For

A quick caveat: Always get your pet’s lumps checked by a vet. This article is not intended as an alternative to a veterinary consultation, and is for information purposes only. Some nasty lumps can disguise themselves as harmless ones, so the guidance below isn’t foolproof. Signs that should make you especially sit up and take notice include:

 #1 Rapid Growth

A rapidly growing lump is potentially worrying. Not only can rapid growth be a sign of an active cancer, but a large lump is more difficult to remove without leaving cancer cells behind.

Size in itself is not necessarily a red light to worry. Some fatty lumps can be extremely large but are rarely anything than inconvenient or unsightly for the dog. Also, some skin cysts can be quite large. However, both of these tend to be slow growing.

#2 Irritating the Dog

Does the lump irritate the dog?

Certain types of lump are uncomfortable and cause the dog to lick or scratch at it. The biggest worry here are skin lumps called mast cell tumors. The latter can release chemicals (histamine) that make them extremely itchy. It’s important to get these diagnosed and removed, since these can be potentially aggressive tumors.

But don’t panic and immediately assume the worst, because there are other explanations for an itch. For example. In-growing hairs or a grass seed foreign body can cause discomfort.

#3 Discoloration

Is the lump discharging or a different color to the skin?

Darkly pigmented lumps can be a sign of melanoma and needs checking urgently. But sadly, a pink lump doesn’t mean you’re home free, because as we said before it’s not possible to tell from the outside.

#4 Wobbly or Well-Attached?

A lump that is glued to the tissue beneath the skin is more worrying than a lump that is within the skin and can be lifted between your finger and thumb.

Likewise a lump that’s an irregular shape is more worrisome than a small, round lump.

Drawing it All Together

Let’s take the two extremes,

Less worrying (When occur all together):

  • Very small (such as pea-sized)
  • A round shape
  • Nicely contained within the skin
  • Not troubling the dog (indeed, they aren’t aware of it)
  • Has been present for months or years without change

More worrying (If one or more of the following are present):

  • Large or rapidly enlarging in size
  • An irregular shape
  • Deeply attached to the tissues under the skin
  • Itchy

But nothing is in life is this straightforward.  Many lumps fall somewhere between these two extremes. And you guessed it. The only way to get an answer is to visit the vet.

Types of Tests

How does a vet find out:  “What is this lump?”

They have a number of ways to do this.

Fine Needle Aspirate (FNA)

What is a fine needle aspirate (FNA)? 

This is the opposite of giving an injection.  The equipment is the same, a needle and syringe, but instead of putting something in the vet sucks back. The idea is to use suction to vacuum a sample of cells into the needle hub. This sample is then squirted onto a microscope slide, and look at under a microscope.

This technique is super simple, isn’t painful, and can give a quick answer.

What’s not to like?

Well, sadly, some lumps do decline to yield up their secrets on an FNA. If their cells are tightly glued together, they can resist being sucked into the needle, so there’s nothing of value to see under the microscope.

Also, there’s an element of luck in a FNA.  Everything hinges on the sample inside the needle being representative of the lump as a whole.  This has been likened to guessing the flavor of a birthday cake just by tasting the icing.

But on the plus side, if the FNA hits lucky and sucks up cells that give an answer, this could mean the dog can skip a more invasive test.  Also, FNAs can give a super-quick answer for problems such as fatty lumps (lipoma) since fat cells are very obliging when it comes to being sucked up. Plus if the lump contains fluid (such as serum, blood, or pus) this can also give a super-quick answer.

Excisional Biopsy

If the lump is small to medium size and has pressed a few alarm bells, the vet may suggest excisional biopsy. This simply means surgically removing the whole lump and then sending it for analysis. This not only gets rid of the problem, but gives you an answer all at the same time. Nice!

However, there are occasions when the vet will prefer to get the full picture before removing the lump. If this is the case then a biopsy has the edge.


A biopsy involves taking a small amount of tissue, rather than the whole lump, to send to the lab. There are many reasons for doing this, some of which are:

  • Biopsy can sometimes be done under sedation, rather than a full anesthetic for removal. This is advantageous if the patient is elderly and the lump would only be removed if it was aggressive.
  • Knowing what the lump is ahead of surgery gives the surgeon valuable information about how much tissue needs to be removed to get rid of the lump completely.

Sometimes surgery isn’t the best option, but chemotherapy or radiotherapy is advisable. Knowing this could avoid putting the patient through unnecessary surgery.

A Lump Isn’t Always a Tumor

And last but certainly not least, when you find a lump don’t panic. Not all lumps are a cancer. If you’re lucky that small swelling may be a cyst, a reaction to a foreign body, or even an abscess. But here’s the rub, don’t just trust to luck, instead seek an expert opinion and see the vet.