Client Information Sheet Copyright Bilton Veterinary Centre© 2011. All rights Reserved Mammary Gland Tumours in Dogs and Cats What are mammary gland tumours? A tumour is defined as an abnormal growth and/or proliferation of atypical cells. The term tumour is synonymous with the word cancer and is a huge umbrella term covering a large number of very different conditions. As the name suggests, a mammary tumour is an abnormal growth of mammary tissue. They are common in dogs and cats, in particular those animals that have not been neutered or were neutered later on in life (particularly after their second or third season/heat). They can occur at any age, but are more common in older animals, and the incidence is highest in female animals, although occasionally male animals may also be affected. All tumours in general can be classified into two groups: • Benign – generally slow growing, non invasive and low risk of spreading to other parts of the body. • Malignant – generally grow rapidly, are often invasive into surrounding tissue, and commonly spread to other remote parts of the body (lungs and liver for example) What are the symptoms of mammary gland tumours? Mammary tumours are similar to breast tumours in people. Usually no symptoms occur other than finding a “lump” when stroking your dog or cat. Uncommonly, mammary tumours can bleed or become infected. Because some of these tumours are malignant, they can spread to other parts of the body and cause illness, loss of appetite, weight loss, or lethargy. Dogs and cats have a linear mammary system with usually 5 nipples on each side (total of 10 nipples), which extend from the groin area, up to the chest area. Masses can occur at any position and can involve either single or multiple areas. By Joel Mills (own work)
Mammary lump in a dog. You can see the lump underneath the nipple and the skin is red and inflamed.
What tests are needed? The diagnosis of a mammary gland tumour relies on clinical judgment and possible evaluation of a biopsy. A reasonable rule of thumb regarding mammary gland tumours in dogs, is that about 50% of these tumours are benign and 50% are malignant. Of the malignant tumours in dogs, around 50% can be cured with surgery alone. Unfortunately, mammary gland tumours in cats are almost always malignant. In dogs and cats, the smaller the tumour is at the time of diagnosis the better the outcome. Copyright Bilton Veterinary Centre© 2011. All rights Reserved
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Client Information Sheet Copyright Bilton Veterinary Centre© 2011. All rights Reserved One of the main factors when decided on the best course of treatment of mammary gland tumours is assessing the risk/evidence of secondary spread (called metastatic spread). Unlike benign tumours, malignant tumours can often spread in two ways: 1. Local Spread. This means that it may invade the surrounding tissue around the initial (called the primary tumour). This is usually taken into account during surgery by both removing the main mass, as well as taking extra margins of “normal” tissue around the edge of the tumour to catch any local spread. 2. Distant Spread/Metastatic Disease. This is where the tumour has either spread into the blood stream or lymphatics and has spread to a site distant from the original tumour. These tumours are called metastases or secondaries. In theory metastases can occur in any location, however we commonly see them in lung(most common), liver, lymph nodes, brain, and bone. If we are concerned about the risk of metastases, then further tests will be advised. These may include: ƒ X‐rays of the chest and abdomen (most likely with malignant mammary tumours) ƒ Abdominal ultrasound ƒ Biopsy of lymph nodes that drain the site of the tumour ƒ Fine needle aspirate of lymph nodes that drain the site of the tumour Chest x‐ray of a dog with mammary tumours. This dog ƒ Blood work to evaluate overall health of was showing evidence of “cannon‐ball” lesions in the pet chest, consistent with metastatic spread to the lungs. Do you decide to treat? Unfortunately, we cannot determine if a tumour is benign or malignant on examination alone. This often has to be done by histological examination of the tumour itself. If necessary a biopsy can be taken prior to surgery (often with large masses), but with smaller masses we will usually perform the surgery and then send the lump away post‐surgery for histology. Often surgery involves the removal of a large amount of tissue, and so quite often there are quite large wounds to heal. For this reason, the choice of operation and the post‐operative recovery time does depend a lot on: • The size of the tumour at the time of diagnosis. • The amount of mammary tissue affected. • If evidence exists of metastatic spread of the tumour to the lungs, lymph nodes, or other sites of the body. • Characteristics of the tumour on microscopic examination (histology). In some instances, surgery may be followed up with chemotherapy. This is rare and beyond the scope of this fact sheet. Your vet will talk to you about this option, should the need arise. Copyright Bilton Veterinary Centre© 2011. All rights Reserved
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Client Information Sheet Copyright Bilton Veterinary Centre© 2011. All rights Reserved What does the treatment involve? In nearly all cases, surgery is the treatment of choice. There are several types of operation performed: • “Lumpectomy” – this is where a small localized lesion is removed. It may or may not involve a nipple • Mastectomy (or mammary strip) – this is where one entire side (chain) of mammary tissue is removed. • Bilateral mastectomy (or bilateral mammary strip) – this is where both sides of mammary tissue is removed. This is such a big operation, that it is usually performed in two stages. Allowing the animal to recover from one side, before attempting surgery on the other side. • Spaying. As a lot of mammary tumours are hormone responsive, it may be advisable to neuter/spay your pet. By removing the source of the hormones (the ovaries) you may drastically reduce the chances of further tumour growth. What is the prognosis? The prognosis depends on a series of factors outlined below: Better Prognosis Worse Prognosis Benign type of tumour Malignant type of tumour No evidence of regional spread to lymph nodes No evidence of secondary spread to distant areas (lungs, liver etc) Quick and early diagnosis Evidence of regional spread to lymph nodes Evidence of secondary spread to distant areas (lungs liver etc) Slow diagnosis Small size Larger size Otherwise fit and healthy pet Older, or debilitated pet or other concurrent illness With early diagnosis and successful surgery, most animals recover well from the disease and often go on and live a perfectly normal and happy life. Copyright Bilton Veterinary Centre© 2011. All rights Reserved
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