Mammary Carcinoma

Mammary Carcinoma2018-09-06T22:58:34+00:00


Breast cancer in female dogs and in women is common. The disease in dogs is more commonly known as canine mammary carcinoma or mammary gland adenocarcinoma. This tumor is the most common cause of death and the most common cancer in the unsprayed dog. The tumor is also quite common in dogs that were spayed late in life because exposure to female hormones early in life increases the prevalence of this tumor. About half of mammary tumors are malignant and about half of the malignant tumors have metastasized at the time they are first diagnosed. The great news is that most dogs with breast tumors are cured with appropriate surgery.


As mentioned above, it is the non-spayed female that is the most likely to develop this cancer. This is especially true as the dog ages. Of the dog is spayed before her first heat (estrus) the risk of canine mammary carcinoma is only 0.05% – very low. After the first heat cycle it goes to 8%, and climbs dramatically to 26% if spayed after the second estrus. In contrast, male dogs are only at a 1% or less risk for this cancer.

If a dog is spayed after initial diagnosis, some studies show that the survival rate is higher than those who remain intact after diagnosis.


The most common clinical sign includes one or more masses or a thickening of the breast tissue. There may be discharge from the nearby nipple. Most breast tumors do not spread and most are cured with surgical resection of the tumor.

While most dogs with breast tumors are cured, a small percentage of tumors are aggressive, including a rare type of mammary carcinoma called inflammatory carcinoma This uncommon form of the disease is not only highly aggressive but progresses very fast. Its symptoms mimic mastitis (mammary gland inflammation). The skin will often be red, swollen, inflamed, and painful. These tumors are highly metastatic and warrant a grave prognosis.


Most frequently a bump or mass is found in a routine wellness exam, or by a groomer or the owner themselves. They generally start small and grow. It is not uncommon to find more than one tumor, since estrogen exposure promotes tumor growth as the years go by.

Blood work, including a CBC and chemistry screen should be done, as well as three-view chest X-rays, urinalysis, and a lymph node biopsy, if possible. In some cases, ultrasound of the abdomen is also recommended.

As with breast cancer in humans, early detection is the key to successful treatment and a positive outcome.


Surgery is the first line of defense for mammary carcinoma. The prognosis however, depends on several factors; the size of the tumor, the type, the grade, and the presence of metastatic disease. In cases that are more advanced, tumors that are more aggressive, or tumors that involve the lymph nodes, chemotherapy will more than likely also be recommended. The hope here is to reduce the risk of recurrence and spread of the disease.


Always remember, the most important thing to beat mammary carcinoma is early detection. Keep up with those wellness checks, and examine you pet often, looking for anything out of the ordinary. Also, if your dog is acting at all abnormal (for that individual), better safe than sorry. Take it to a vet to be looked at.