Pet Factsheets

Mammary gland adenocarcinoma

Mammary gland enlargement is a common sign of this condition in rabbits
©Richard Saunders

A mammary gland adenocarcinoma is a malignant (cancerous) growth of the glandular tissue affecting the mammary glands. One or more glands may be affected. They often metastasise (spread) to other areas of the body, commonly the lungs, but can spread to the liver and other abdominal organs.

What causes them in rabbits?

They are often related to uterine hyperplasia and adenocarcinomas.

What are the signs?

Most rabbits with mammary gland adenocarcinomas are clinically active, alert and may be eating and passing droppings as normal. If there is spread, and especially to the lungs, the rabbit may be depressed, lethargic and show some signs of abnormal or respiratory difficulty and weight loss.

Commonly rabbits have mammary gland enlargement, and there are masses that can be easily felt in the mammary glands. Often these feel solid, are non-painful and there may be some brown/red discharge evident from the teat(s) of the affected gland(s).

Are they common?

The risk increases with age and commonly they affect entire female rabbits, or those spayed later in life, from 2 years of age onwards. There are no reports of the condition happening in male rabbits, but theoretically this would not be impossible. Any breed may be affected, but Belgian Hares and English breeds of rabbits seem to be more commonly affected.

Can they be prevented?

Largely spaying at a young age will help to prevent them. The longer a female rabbit stays entire, the higher levels of circulating hormones are present, which are largely responsible for the development of the tumours. Therefore spaying, when the rabbit is young, fit, and healthy will massively reduce the risk of them occurring later on in life (plus removing the risk of uterine adenocarcinoma).

How can my rabbit be treated?

Firstly, your vet will want to confirm a diagnosis. They will need to take a fine needle aspirate (a type of biopsy procedure) of cells from within the masses. This can be done with the rabbit conscious and is no more uncomfortable than having an injection.

The cells can then be sent off to a lab to be examined to see what they are, and a diagnosis made. If they come back as being an adenocarcinoma, your vet will want to take some chest and abdominal x-rays to ensure there has been no obvious spread to other organs. If there has then surgery is not usually an option and palliative care, or euthanasia will be the only options.

If there is no spread, then surgically removing the mammary masses and affected glands and spaying the rabbit (if not already done) is the treatment of choice. If there are several mammary glands affected, the surgery may be too invasive to perform in one go, and more than one surgery may be required.

What is the prognosis?

If there is no spread to other organs, the prognosis following surgery is good, however there is always the risk that spread may have occurred but could not be detected on x-rays.

Sadly, if the cancer has already spread to other areas of the body, the prognosis is poor and if the rabbit cannot be kept comfortable, then euthanasia should be performed to prevent further suffering.

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