Have you ever found a lump
on your pet? This week I’m running a two part series on lumps in companion
animals. What are they? What should you do about them? Can you just ignore them and hope they will go away?
It’s very common for an
animal to present, either directly for the purposes of examining a lump OR
incidentally (e.g. a vaccination, and by the way – is this lump anything to
worry about?).
Part 1 – What is this lump?
I’ve
found a lump on my pet. What should I do? Don’t panic. Veterinary
patients commonly present with lumps, of which there are many causes. A lump is
a collection of cells in the skin (a cutaneous lump), or in tissue beneath the
skin. Broadly speaking, lumps can be non-cancerous (for example, an abscess
(pus), hematoma (blood) or inflammatory reaction (for example, hives or
urticaria), or cancerous (neoplastic). Very occasionally a lump actually contains
a foreign body. For example, when I removed a lump from the armpit of a dog, I
found it contained part of a kebab stick which had migrated from the gut through the
abdominal wall. I have to confess that was a very satisfying lump to remove.
![]() |
Better out than in: the tip of a kebab stick was found in a lump in the armpit of a dog. |
Cancerous lumps may be
benign or malignant. There is no way to determine if a lump is cancerous just
by looking. Cancer is a tissue diagnosis. That means that a biopsy is required
to determine whether cancer is present.
The good news is that many
cancers can be cured with early treatment. Contact your vet and arrange an
appointment.
Can some lumps go away by themselves? Occasionally, but this is the EXCEPTION rather than the rule. For example, puppies may develop histiocytomas which can disappear. Similarly, warts (or papillomas) may occur (especially in puppies) then disappear over the course of a few months.
![]() |
A close up of a large wart in a dog (the diagnosis was confirmed by histopathology). |
It’s
only a small lump. Should I just keep an eye on it? While
it can be tempting to “wait and see” if a lump changes or grows bigger, if the
lump is cancerous then there is a real risk that the cancer will progress and
may spread to other sites in the body during this waiting period. The earlier a
diagnosis is made, the better the outcome. The size of a lump alone cannot be
used to determine whether or not it is cancerous.
It’s
been there for ages. Sure, but that doesn’t mean it isn’t nasty.
Cells in a lump can transform into cancerous cells over time. In some cases
cancers are slow growing. Being around for months or years doesn’t mean a lump
is harmless.
![]() |
This benign fatty tumour (a lipoma) grew so large that it affected the dog’s movement. Surgery to move very large lumps like this is much more complicated. |
Can't you tell me if its cancer just by looking at it? In short, no. Cancer is a tissue diagnosis. You need to examine cells or tissue to make a diagnosis of cancer. Sure, if its full of pus its more likely to be an abscess. Even more so if the patient is a cat who has just been bitten by another cat. But lumps can be misleading. Tumours often develop "necrotic centres" and may appear to be abscesses.
![]() |
A malignant mast cell tumour on a dog that has been shaved for surgery. The circle around the lump indicates the extent of margins required to ensure the tumour is removed locally. |
What
does a biopsy involve? There are different biopsy techniques,
ranging from a needle biopsy (where cells are removed from the mass for
examination on a slide), to incisional biopsy (a piece of the tumour is
removed), to excisional biopsy (the entire tumour and a barrier of normal
tissue are removed). The type of technique used depends on the location and
size of the lump. Where possible, we take a biopsy prior to performing any
other surgery. There are exceptions to this rule: for example, where a lump is
found in the testes we usually remove both testes by castration (this is an
excisional biopsy).
Sometimes the result
will suggest that surgery is not required. For example, in the case of small
fatty deposits or cysts, surgery may not be required. Alternatively, in the
case of some cancers like lymphoma, medical rather than surgical treatment is
used most commonly (with rare exceptions).
Why do you recommend sending biopsies for histopathology? Because cancer is a tissue diagnosis. The most accurate information about whether something is a tumour or not, or what type of tumour it is, is gleaned from histopathology in most cases. The pathologist can look at the cells within the tissue architecture they are invading, and in most cases can identify what is going on – what sort of disease is present, what cells are involved, how aggressive is it (tumours can be graded). From this information decisions can be made about how big surgical margins should be to give the best chance of eliminating the disease. There is a tendency for some clients to see histopathology as an optional extra. In fact it provides valuable information. Removing a lump without doing histopathology is, in some ways, like taking an x-ray and not looking at it. If I perform a biopsy on any of my animals (and yes, I have done so) it goes for histopathology. I want to know what I am treating.
Why do you recommend sending biopsies for histopathology? Because cancer is a tissue diagnosis. The most accurate information about whether something is a tumour or not, or what type of tumour it is, is gleaned from histopathology in most cases. The pathologist can look at the cells within the tissue architecture they are invading, and in most cases can identify what is going on – what sort of disease is present, what cells are involved, how aggressive is it (tumours can be graded). From this information decisions can be made about how big surgical margins should be to give the best chance of eliminating the disease. There is a tendency for some clients to see histopathology as an optional extra. In fact it provides valuable information. Removing a lump without doing histopathology is, in some ways, like taking an x-ray and not looking at it. If I perform a biopsy on any of my animals (and yes, I have done so) it goes for histopathology. I want to know what I am treating.
Tune in tomorrow when we talk about treatment of lumps.