Breast Cancer in Dogs | Diagnosis, Treatment & Prognosis

Picture of a dog with a ball

Spaying significantly reduces the chances of breast cancer in a dog. In females that are spayed before their first heat cycle, mammary cancer is extremely rare as the risk of developing it is close to 0.05%. However, it is around 8% for dogs that are spayed after one heat cycle and around 26% for dogs that are spayed after they enter heat for the second time. Hormonal factors increase the risk of this type of cancer, as well as genital cancer, too, and that is why it is recommended that you spay your canine companion before the first heat cycle.

One thing that we have to get out of the way right from the beginning is that male dogs can get mammary cancer, too, although in their case, the incidence is much, much lower compared to that in females.

There are many kinds of breast tumors in dogs, and in this article, we will discuss some of the common ones, the clinical signs of the disease, the treatment options, as well as its prognosis.


Around half of all mammary tumors in dogs are benign while the other half are malignant. To choose the right treatment for the dog that is suffering from cancer, the vet will have to determine the exact type of cancer.

It’s quite rare for a single tumor to contain only one type of cancerous cell. Usually, it is a mixture of glandular and connective tissue, which means that part of it can be benign and part of it can be malignant. Benign tumors include fibroadenomas, duct papillomas, and simple and complex adenomas.

Malignant tumors can include tubular, papillary, and papillary cystic adenocarcinomas, anaplastic and solid carcinomas, osteosarcomas, fibrosarcomas, and malignant mixed tumors.


When tumors arise in the mammary tissue, they can be detected by palpating the mammary glands. They can be observed either as a single, solid mass or as multiple smaller ones. Many neoplasms are known to grow rapidly over the course of several months.

The symptoms of breast cancer in dogs differ depending on the cancer’s nature. While benign growths are slow growing and are smooth and small, malignant ones grow rapidly, are firmly attached to the skin and they have an irregular shape. Sometimes, they can grow so fast and are so aggressive that they can even ulcerate the skin, in which case the signs of breast cancer in dogs are obvious.


The health status of the dog needs to be assessed first, and this is necessary because if it’s bad, the animal might not be able to go through any type of treatment and then survive. Many breast tumors can be detected either annually when you take your pet in for a checkup, or sometimes, they can be discerned by the pet parent because they feel something lumpy in the dog’s mammary glands.

Blood and urine samples are often required for analysis as they can be used to detect any abnormalities which can suggest that the dog’s health has been affected. The tumors might be measured, as well, and they might also have to be assessed as to whether they are fixed or they float. Following the physical examination, your dog might have to go through several diagnostic procedures which are necessary for telling the exact type of cancer, its stage, and whether it is malignant or benign.

These procedures range from biopsy and cytology to X-rays and abdominal ultrasounds. Imaging methods can reveal whether the tumor has spread to other organs. Sometimes, more advanced radiological techniques (like CT scans) or MRI can be used if they are available. They can be quite expensive, however, but they are highly sensitive and they can effectively determine the location of metastases.

Most masses that have developed in the chest are spread to the lungs while those that have grown in the abdominal area spread to abdominal organs.

Treatment Options

There are three types of treatment that can prove to be useful. Surgery is performed in almost all of the cases, whether the tumor is benign or malignant, except those situations where the health status of the animal does not allow the operation to happen.

Depending on the number of tumors, their size, and their location, the vet might choose a specific type of surgical removal. This can mean that the tumor and part of the surrounding healthy tissue is removed, that the entire mammary gland that has been affected is removed, or that uni or bilateral mastectomy is performed (all of the glands on one or both sides of the body are removed).

Chemotherapy involves treating the cancer by using medical drugs which target the rapidly dividing cells and then kill them. This treatment method does have several side effects, and it might or might not make sense to opt for it depending on the severity of the disease or the dog’s health status. Sometimes, a combination treatment consisting of surgery and chemotherapy can prove to be effective.

Radiation therapy is performed less often, but it can be highly effective, as well. However, it could cause skin lesions, so it needs to be performed with care. All dogs that have cancer should receive pain medication no matter the treatment option.


When it comes to breast cancer in dogs survival rate, the prognosis is good or even very good if the canine patient has a benign tumor. For dogs that have malignant masses, however, the outlook differs a lot on the tumor type, its stage, and even its size. The life expectancy can range from several months for highly aggressive tumors to three years or more for those that have been discovered in due time.

Preventing Breast Cancer in Dogs


The best way of preventing breast cancer is to choose to spay your pet before he or she enters the first heat cycle. The second prevention method consists of looking out for breast cancer in dogs symptoms as often as possible.

Be mindful when petting your dog’s belly and chest and gently palpate the skin to see whether you can’t feel anything lumpy and suspicious. Do this affectionately, as if you’re petting your canine friend, but do it regularly, especially if you haven’t spayed your female dog before her first heat cycle.

Given that cancer can be caused by a wide variety of factors, it’s very hard to tell what you can actively do to prevent it. When it comes to nutrition, you can at least try to feed your canine companion food that is as natural as possible, and by this, we mean artificial colors and preservative-free.



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