Mammary tumors in dogs


Mammary tumors represent at least half of all tumors found in dogs. They appear on average around 10 years of age. They are predominantly intact (unsterilized) or late sterilized females who suffer from it. These tumors are rare among males and young animals.

Early sterilization confers good protection against this type of tumor. Here type of tumor. Here are some interesting figures: sterilizing a female before her first heat reduces by 20 % this risk. After two heats, there is no impact on risk reduction.

50 % of mammary tumors are found to be benign upon diagnosis in the female dog. Even though they are less frequent in males, the tumors tend to be more aggressive ( malignant).


Upon physical examination :

- Presence of one or more firm and nodular masses. In over 50 % of cases there is no more than one gland involved.
- The masses can be found anywhere on the chain of mammary glands, but they are more frequently caudal glands.
- The masses can be of variable size (a few mm to several cm).
- Some times the masses are adhered to the tissues un depth and not mobile.
- In 25% of cases we can observe an ulceration of the skin at the site of the mass .
- There may be the presence of abnormal discharge from the nipples of the affected glands .
- In some cases, we may observe an increase in the volume of the lymph nodes draining the affected region (regional auxiliary or inguinal lymph nodes).
- Cachexia in advanced cases.
- The rest if the examination is usually normal.

The method of choice to confirm the diagnosis is undoubtedly exisional biopsy. This consist of removing the entire mass in surgery and submitting it for analysis (histopathology) to an external laboratory. Another method, cytology after fine-needle aspiration, often yields results which are more or less conclusive. It is obtained by pricking the affected tissue with a needle in order to collect cells. These will be spread on a slide and then observed under a microscope.

Before any surgery to remove one or more mammary tumors, it is recommended to perform chest radiographs. In the lungs, blood circulation slows to allow a better blood oxygenation. This slowing of blood flow allows the circulating tumor cells to infiltrate the lungs which are the principal site of metastasis.


Treatment consists of the surgical excision of the tumor or abnormal tissue. Different techniques are possible, from excision of the masse or nodules only, to the excision of one or several mammary glands (simple mastectomy and radical mastectomy). If the female is still fertile, it is possible to sterilize at the same time . It should be noted however that there is no difference in survival time in dogs who underwent sterilization before or simultaneously with a mastectomy alone.

A denocarinoma is the most common malignant tumor in dogs. The prognosis following surgery is variable depending on the lymphatic vessels. It also varies depending on the differentiation of cells and tumor size ( better prognosis if it measures less than 3 cm in dogs).

After surgery, chemotherapy may be recommended to provide a better survival time for your pet.