Mammary cancer is the presence of a tumour or multiple tumours in the mammary glands. There is a very high risk factor for intact females, especially as they age and go through multiple cycles of heat. Lumps or masses can be benign or malignant and both require medical treatment. It is almost split right down the middle the number of cancerous versus non-cancerous tumours that develop. Once a tumour develops, the dog is much more at risk for developing more. The mammary glands provide and produce milk for puppies. They are found under the chest all the way to the groin. There is evidence that points to the fact that some dogs are genetically predisposed to developing mammary cancer. Tumours usually show up as a mass that can be a single small mass or a bunch of tumours grouped together. Some masses are hard to move and feel as though they are attached to the body while others move easily. When looking for lumps the glands in the groin is usually where they can be found. Early detection is key with mammary cancer as it can often be treated when caught early enough.

Like with most cancers, pinpointing an exact cause isn’t possible. It is believed that genetics and hormones play a role in mammary gland cancer. As well, the age of the dog when spayed will either significantly increase or decrease the dog’s chance of developing a tumour(s). The older the dog is when spayed, the more likely it is to develop the condition.

There is no surefire way of preventing mammary gland cancer however spaying a dog early will significantly reduce the dog’s chances of developing tumours. The key is to have the dog spayed before its first heat.

Symptoms to watch for include:

  • a tumour/growth, whether it be a solid mass, a single lump or multiple swellings located in the mammary gland tissue;
  • the tumour or mass, may be easy to move, which usually points towards a benign growth;
  • superficial loss of tissue on the skin over the mammary tissue;
  • inflammation of mammary glands;

The tumour or mass may seem to be fixed to the body or skin, which usually points towards cancerous or malignant growths. Benign growths are often slow growing, small and smooth. Malignant growths are often irregular in feel and shape, grow quickly and seem to be attached to the skin or body underneath.

Dogs at Risk
Female dogs who are not spayed run the risk of developing mammary cancer. As well, those females who are spayed later in life also have a much higher instance of developing tumours. For dogs that are spayed before their first heat, there is almost zero risk of mammary cancer. Other risk factors include genetics and obesity. There are certain breeds that are at higher risk which include the English Setter, Boston Terrier, Brittany Spaniel, Pointer, Cocker Spaniel, and the Fox Terrier.

Testing and Diagnosis
For a confirmed diagnosis testing will be necessary. The veterinarian will likely begin with a complete blood count, urinalysis and chemical blood profile. The tumour will need a biopsy to conclude if it is malignant or benign. As well, to check for metastasis x-rays will need to be done on the abdomen and chest. An abdominal ultrasound will shed more light on the dog’s condition as well.

Treatment and Prognosis
Surgical removal is often practiced when a tumour is found whether it be a malignant or benign tumour. In some cases removing more than the mass is necessary and the veterinarian will also remove the lymph nodes and mammary tissue. As well the vet will often spay the dog during surgery. If the biopsy shows a malignant tumour the veterinarian will then need to determine if metastasis has occurred. Tumours can spread to the lungs or lymph nodes if they are aggressive. In half the cases, by the time a malignant tumour receives surgery it has spread. When the biopsy shows the tumour as being benign, treatment usually just means removal of the mass. There are a number of different surgical procedures the veterinarian may use. A lumpectomy means the removal of the rim of normal tissue and a small tumour. A unilateral mastectomy will require the removal of the five mammary glands. Meanwhile a simple mastectomy means the entire mammary gland is removed during surgery.

If the cancer is caught early and surgery is performed, in half the cases it can be removed completely. With mammary cancer immunotherapy and chemotherapy are not usually suggested as it does not cure the cancer. Prognosis of the dog depends largely on what kind of tumour is present, whether it be benign or malignant. Other factors include if it has spread and if so where, as well as the size of the tumour.