Lumps & Bumps In Pets

Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS

Table Of Contents

 - Overview
 - Diagnosis
 - Treatment

Most pets will develop a lump on or under the skin at some point in their life, and some pets may develop several. Lumps filled with fluid are commonly referred to as cysts. The fluid can be watery or very thick and pasty, but these are not usually a cause for concern. Lumps that are solid are often referred to as tumours, which simply means that the lump is an abnormal growth of cells. Tumours can be innocent (benign), such as warts or fatty lumps, or more aggressive (malignant), such as some types of cancer. 

How are lumps and bumps diagnosed? 

It is impossible to know for certain what a lump is just by looking at it. Many different types of tumour can look and feel identical, especially those that sit under the skin. It is strongly recommended to test all lumps, so that we can make an informed decision about treatment. We may decide that no treatment is required if the lump is benign, but we cannot know this is appropriate just from looking. It is particularly advisable to test lumps that have newly appeared, or are growing quickly. Sometimes it is worth re-testing a lump if its behaviour unexpectedly changes, such as sudden growth after a long period of staying the same. 

There are two common ways that we can test and diagnose a tumour, each with advantages and disadvantages. 

Fine Needle Aspirate (FNA) 

This test involves taking a sample of cells out of the mass using a needle. The cells are transferred on to a microscope slide for examination. This may be performed in-house, but often the sample is sent to a specialist pathologist (experts in tissue analysis). They will identify the type of cells present, which can tell us what the tumour is and where it is likely to be growing from. 

The procedure itself is quick and often painless, as the needle used is only the same size as that used for a vaccination. It can usually be performed with the animal awake, sometimes during the consultation. Occasionally, this isn’t possible, especially if the mass is somewhere difficult to reach or very sensitive, such as near the eyes. 

The main disadvantage of an FNA sample is that not all lumps will exfoliate cells easily, so there is a chance of a negative or inconclusive result. FNA sampling is ideal for soft masses, and fatty lumps (known as lipomas) are almost always identifiable by this method. FNA sampling is less good for very firm masses, where a result is less predictable. FNA sampling is also sometimes not possible if the mass is very small, or very deep, as it can be difficult to get a reliable sample. 

Tissue Biopsy 

A tissue biopsy involves taking a piece of the lump, usually surgically. Again, the sample will be sent to a specialist pathologist at an external lab. The pathologist will look at the type of cells present, but also how those cells are interacting with each other. This not only identifies the type of tumour, but can also provide valuable information, such as how the tumour is likely to behave. 

A biopsy is always taken under sedation or anaesthesia, depending on the type and location of the lump. For this reason, there are slightly more risks involved compared to an FNA, and the costs are higher. The advantage of a surgical biopsy is that the surgeon has more control over which area is sampled, and we will almost always get a diagnosis. 

It is always preferable to diagnose a tumour before we try to remove it, so that we can be sure we are choosing an appropriate treatment plan with a good chance of success. Sometimes, if a mass is very small, we may remove it all during the biopsy. This is known as an excisional biopsy, and is only suitable under certain circumstances. 

How are lumps and bumps treated? 

Treatment will depend largely on the findings of the FNA or biopsy. Benign growths, such as fatty lumps, may not require treatment and can be monitored instead. Surgical removal may be advised if the mass is growing, or is causing problems, such as being sore, infected or ulcerated. 

Surgery may achieve a cure for some cancerous lumps. Further testing may be recommended before (or after) surgery to gather more information. Sometimes, there are several options available, and your vet will discuss a plan specific for you and your pet, taking the type and location of the tumour into consideration. 


Please note that the content made available on this webpage is for general information purposes only. Whilst we try to ensure that at the time of writing all material is up to date and reflects industry standards, we make no representation, warranties or guarantees that the information made available is up to date, accurate or complete. Any reliance placed by yourselves is done so at your own risk.

Page last reviewed: 27th March 2024

Next review due: 27th March 2026