What is a lump and what causes them?
Lumps and growths on dogs come in all shapes, sizes and locations and are quite common in canines. Not all lumps are ‘growths’. Sometimes the cause of the swelling may be an abscess, cyst, seroma (fluid-filled swelling sometimes seen after a knock or after surgery), an area of inflammation or callus (thickened skin due to rubbing) etc. An examination will usually be able to determine if this is the case and then appropriate treatment can be provided.
Generally, it is impossible to give a 100% accurate answer as to what a growth is just by examining it, although it may be possible to suggest what it is likely to be, and therefore, depending on the appearance of the lump, your vet may advise on further testing.
Lumps vs tumours
The word ‘tumour’ is a very emotive word and is associated and used often when diagnosing lumps in dogs. The word originates from the Latin ‘tumor’ which means ‘swelling’ and therefore technically it could be used for any swelling on the body.
In veterinary, however, we do generally tend to use the word to describe a growth – this could be equally applied to a benign growth (or lump) as much as a malignant (cancerous) growth, therefore if we describe a growth as a tumour, this does not necessarily mean that it is cancerous.
How common are lumps on dogs?
Lumps are a very common occurrence on dogs and is a good reason for us to examine our pets regularly. There are many types of lumps and growths and while some may be unpleasant for dogs, many are not.
How to treat lumps on dogs
If it appears that a lump genuinely appears to be a growth, the next consideration will be to decide on an approach. Options for further investigation may include:
Fine Needle Aspirate (FNA)
Fine needle aspirate involves inserting a needle into the growth to remove some of the cells. These are then transferred onto a microscope slide to allow examination under the microscope (cytology). The advantage of FNA is that it allows investigation of a lump without having to resort to anaesthesia and more invasive techniques. Often this procedure is done while your dog is with you in the consulting room and it’s usually not painful, meaning it is uncommon for the animal to need sedation or anaesthetic for your vet to carry this out. It may not be appropriate in some cases, particularly if a growth is very close to a sensitive area or if your pet is in pain around the area, and it may also depend on your pet’s temperament.
In a lot of cases, FNA can provide useful information about a growth which will then inform your vet’s next steps, i.e does it need removing, and how big a margin around the lump do they need? The disadvantage is that in a small proportion of cases, the sample may provide no useful information; some lumps may not shed cells very easily and may not provide a representative sample. How accurate the answer also depends on where the needle passes into within the lump. In some cases, a lump may have a surrounding fatty tissue. If the needle passes into the surrounding tissue rather than the core of the lump this may provide misleading information.
When do you get the results?
Cytology samples are usually reported to your vet within a day or two if sent to an external laboratory. Some samples may be examined by your vet within the surgery.
A surgical biopsy may give a more accurate answer than a FNA. A surgical biopsy allows examination of a section of tissue and the arrangement of the cells within the tissue (histopathology), as opposed to the FNA which provides cells that have been sucked out and are no longer in their normal arrangement. This may provide more accurate information as to how malignant or benign a mass is. It is a particularly useful technique for certain types of growths which either may not shed cells very easily or when it is important that we know what grade (severity) that the growth is, as this may affect how aggressively we have to treat your pet. The downside to a biopsy is that it usually requires general anaesthesia to retrieve the samples.
How long for surgical biopsy results?
Typically histopathology samples have a slightly longer turnaround in the lab than cytology samples. In most cases, however, the results will be reported back to us within a week or two (depending on the type of sample).
Surgical excision (removal)
Surgical excision involves putting your dog under general anaesthetic and then removing the growth. We then, in most cases, send the growth to the lab for diagnosis (histopathology). The advantage of surgical removal is that the mass is gone. We also get information about the structure and grade of the mass and can also examine the margins of the growth for evidence of invasion into surrounding tissues.
However, in some cases it may be more appropriate to do other investigations first, such as a biopsy, as it may be important to know, prior to operating, how aggressive our treatment needs to be and how big a margin we need to remove around the growth, especially in areas where there is limited skin to allow closure of the wound after removal, such as the lower legs, face etc.
Assessing the reports
When we are assessing cytology and histopathology reports, we are first interested in whether the sample shows that the lump is truly a growth or whether it could be something else such as inflammatory tissue.
Benign or malignant?
The next consideration is whether the growth is benign or malignant. A benign tumour refers to a growth that does not spread and doesn’t invade into the surrounding tissue. These can usually be cured by surgical removal or, if appropriate, may be monitored only.
The term ‘malignant’ describes a growth that is invading into surrounding tissues and that may be expected to spread to other areas of the body (metastasis). This would be generally how we would refer to a ‘cancer’.
Regardless of the result, your vet will discuss any implications with you and talk through the next steps and any further treatment options which may be required.
What to do if you find a lump on your dog
If your dog develops a growth, we would always advise that it is worth booking a free consultation with your nearest Animal Trust surgery to examine the area of concern.