Breast cancer in dogs

Breast Cancer Awareness in Dogs

Mammary tumors (Breast Cancer) in Dogs.

We are all familiar with women’s breast cancer that can affect up to one in nine women. But how many pet owners know that the incidence of mammary tumors reaches one in four unspayed female dogs?

Clinical signs and types of tumors encountered in female dogs?

A mammary gland tumor will generally appear as a painless small lump. It is often discovered in the groin area by either the owner or during the annual check up by the veterinarian. As it progresses the lump becomes a mass that can reach a considerable size as big as an orange, however, in general, it is detected earlier. Ulceration (wound) and necrosis will develop at a very advanced stage.

The good news is that 50% of mammary tumors will be benign ones. But since it is not possible to differentiate a benign from a malignant (cancerous) tumor on simple observation of the mass, it is necessary to either perform a fine needle aspiration in order to request a cytological report or have the mass removed surgically and request a more accurate histopathology report from the laboratory.

FNAB (Fine Needle Aspiration Biopsy) is limited to the fact that if the needle is stuck in the wrong part of the tumor (difficult to determine), it will not show any tumor cells and hence give a “false negative” result. We, therefore, prefer to remove the tumor in toto and sent it off for histopathological examination. The results in the report of the histopathologist give us a complete overview of which type of Breast Cancer we are dealing with, what stage is it in and has it been removed entirely. Allowing us a more accurate prognosis and treatment plan can be made and offered.

When discussing tumors, there are several gradations to consider, but the most important difference is whether a tumor is:

If the tumor is cancerous, it will spread to:

The most commonly seen tumors are:

Protection via spaying

Spaying a female dog before her first heat reduces the risk of mammary gland tumor development to less than 1%. Spaying her after the first heat period reduces the risk to 8%. Spaying a female after 2 cycles doesn’t minimise the risk of developing a mammary tumor. Early spaying is therefore highly recommended in our Clinic. Please discuss this with your vet as not all breeds benefit in the same way from early spaying.


Surgery is required in almost all cases and consists of removing the lump(s) with adequate margins of normal tissue (free margin excision – no tumor cells spotted in the histopathologic exam of the tumor after removal). The amount of tissue to be removed depends on the size and location of the tumor(s). This can extend to a full mastectomy, which is the removal of the entire mammary chain on one or both sides including the inguinal lymph node if affected.

Success rate for surgery depends on the nature of the tumor, its size and location. Early detection does also greatly affect the success rate as it allows intervention before the tumor metastasizing to other body parts which are inoperable. Before admitting your dog for surgery, the vet will advise X-rays to be made to ensure metastases has not yet developed, as the tumor requires a different approach should this be the case.

Chemotherapy in dogs is only applied if it adds to a continuation of quality of life of your pet and a reasonable gain of life expectancy. Dogs do not have a similarly long life expectancy as humans do (10-15 years as compared to 75-90 years). Most treatments are very intrusive and cause many side effects, therefore not rewarding a quality of life. Besides this the chemotherapy can also be harming the safety of the family in the pet’s direct environment as excreta (stool, urine, saliva) can contain the chemicals.

Please contact us or use our FREE Mammary Gland examination in October, should you have any concern. During the whole month of October receive 15% discount on spaying of female dogs and cats. Book an appointment at 04 3408601.