Like any animal, rats can, sadly, suffer from cancerous growths. So what do you need to know about this potentially worrying condition?

1) Location, location, location…

Cancerous growths can occur anywhere, from the skin to internal organs in the abdomen (including the reproductive organs), and within the skull or chest. However, by far the most common location of growths or lumps found in rats is those of the mammary gland. Mammary tumours are found in both male and female rats. The mammary tissue in rats extends from inside of the front leg to the abdomen. Mammary lumps can grow quickly and can cause difficulty with movement of the limbs.

2) Symptoms are just as varied

Symptoms of a cancerous growth will very much depend on the location of the growth, and if it is causing any disruption. So, for a mammary lump it might just be seen as an unsightly bulge, however a tumour inside the brain could lead to neurological changes such as wobbliness, a head tilt or differences in behaviour. An abdominal mass could lead to changes in appetite or digestion so the first sign noticed might be that the rat is eating less or losing weight. If the rat is feeling any discomfort due to a cancerous growth it may spend excessive time grooming the area or chewing at its fur in the area. If the area is painful the rat may also become less tolerant of handling even if it is usually very tame.

Occasionally a lump may become ulcerated or the skin over the mass may break open, this can lead to bleeding or discharge from the mass. In the case of an ulcerated lump infection might set in and the rat may become generally unwell with vague signs such as loss of appetite, lethargy, or a hunched appearance.

3) A cancer can be either benign or malignant

Cancer in rats can be divided into either malignant or benign. A benign lump is one which doesn’t spread and usually behaves less aggressively than a malignant growth. If a benign lump is surgically removed this would usually be curative. In the case of mammary masses (the most commonly presented cancer in rats) around 90% are benign fibroadenomas, and therefore surgical removal is usually successful at dealing with it.

A malignant cancer is one which can spread from the original location. This spread can occur before the first tumour has even been detected or noticed. Because malignant growths have the potential to spread, the outcome is usually poorer for the rat as treatment options become less viable or successful.

4) Cancers are common, but the causes are complex

Unfortunately, tumours are very common in rats. There can be an underlying genetic predisposition which can increase a rat’s chances of tumour development. It is known that consumption of excessive calories can predispose rats to certain tumours.

In the case of reproductive organ tumours, neutering can reduce a rat’s risk of developing cancers later in life. The risks and benefits of such surgery can be discussed with your vet.

5) The main treatment option is surgical removal

Treatment of the cancerous growth will very much depend on the location. Some masses will be small and manageable and can just be monitored without any specific treatment. However, in some cases the size or the location of the lump may necessitate treatment, this is usually surgical removal. Mammary masses can for example grow significantly and impact on how the rat moves. Some masses may drag along the ground causing discomfort, or damage to the overlying skin. If a lump becomes ulcerated this usually forces the need for treatment.

In order to surgically remove a cancerous growth a general anaesthetic is needed. Once removed the mass can be sent away to the laboratory for testing to determine exactly what kind of growth it is. Usually, the rat will have buried stitches to prevent them from pulling open the wound. Post operative pain relief would normally be provided to keep the rat comfortable. This hopefully avoids the rat from being bothered by the surgical wound and chewing it, allowing the area to heal.

If you notice any growth or swelling on your rat…

Make sure they get checked over by your veterinary surgeon. It might be nothing serious; however, if it is a cancer, it is usually much easier to treat if identified early.

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