Mammary Cancer in Cats

Mammary gland cancers in cats are similar to breast cancer in humans. Mammary cancer is usually a malignant adenocarcinoma that appears in one or more of a cat’s breasts. Other forms of breast and mammary cancer in a cat include adenomas, duct papillomas, and sarcomas. Females, as well as males, can develop this form of cancer. When it appears in cats, it can be fatal, even if treated with surgery, radiation and chemotherapy. Adenocarcinomas are one of the most aggressive types of cancer, metastasizing or moving to the lymph nodes and other parts of the cat’s body. Siamese cats, cats between the ages of ten and fourteen years of age, and intact (not spayed) females are most likely to develop mammary and breast cancer.

Cat owners and their vets will notice the following symptoms:

• Swelling of the breasts or mammary glands
• Infection in and around the glands and breasts
• Skin ulceration surrounding the masses
• Sores that don’t heal
• Pain
• Fever
• Tumors appear as firm nodules firmly attached to the underlying muscle and skin
• Clear, bloody, or milky discharge from the cat’s nipples
• Dead (necrotic) tissue at the site of the tumor
• Unexplained weight loss
• Unwillingness to eat
• Weakness

Several factors seem to influence why cats develop mammary or breast cancer:

• Leaving cats intact (not spayed)
• Allowing the cat to have several heat cycles or litters before spaying
• Cat’s age (cancer usually begins when cats are between 10 and 14 years of age)
• Hormones: if cats receive medications with estrogen, they are more likely to develop mammary or breast cancer
• Siamese, Persian and other Oriental breeds, as well as domestic shorthaired cats are at higher risk of developing tumors of the breasts or mammary glands at younger ages

When a pet owner brings in a cat with mammary and breast tumors, the vet will conduct a full physical exam, focusing most on the mass or masses. They will palpate the masses and nearby lymph nodes, looking for a spread of the mass. 

Once this part of the exam is done, the vet orders X-rays, which enable them to determine how big the tumors and whether it has spread. In addition, the vet may order an abdominal ultrasound, looking for a spread of the tumor to other organs. They may also carry out a fine-needle biopsy, where they aspirate lymph nodes to check for the presence of cancer cells. They will order a complete blood count and a biochemical profile, which allows them to check on the cat’s overall health. Other diagnostic tests may include urinalysis and a clotting profile of the drawn blood sample. 

If surgery is decided upon, the surgeon may take a small sample of the tumor and send it to pathology for a biopsy, especially if they are sure the cat has mammary or breast cancer. This biopsy allows the pathologist to determine exactly what kind of cancer the cat has.

When a pet owner brings in a cat with mammary and breast tumors, the vet will conduct a full physical exam, focusing most on the mass or masses. They will palpate the masses and nearby lymph nodes, looking for a spread of the mass. 

Once this part of the exam is done, the vet orders X-rays, which enable them to determine how big the tumors and whether it has spread. In addition, the vet may order an abdominal ultrasound, looking for a spread of the tumor to other organs. They may also carry out a fine-needle biopsy, where they aspirate lymph nodes to check for the presence of cancer cells. They will order a complete blood count and a biochemical profile, which allows them to check on the cat’s overall health. Other diagnostic tests may include urinalysis and a clotting profile of the drawn blood sample. 

If surgery is decided upon, the surgeon may take a small sample of the tumor and send it to pathology for a biopsy, especially if they are sure the cat has mammary or breast cancer. This biopsy allows the pathologist to determine exactly what kind of cancer the cat has.

Generally, the prognosis for cats with breast or mammary cancer is guarded, with a few exceptions. If the cat’s tumor is smaller than 2cm, it may survive for up to three years. Cats with tumors between 2 and 3cm may survive fur up to two years and cats whose tumors are larger than 3cm may survive for up to six months. If the cat’s treatment for small tumors that were caught early is aggressive, the cat may live for between two and three years. Cats who underwent large resections (having one or both mammary chains removed) lived post-surgery for up to three years while those cats who had only the tumor removed lived for only one year after surgery.

It benefits the cat to be seen immediately by the vet when its owner detects a suspicious lump.

Over 60 percent of tumors that have been removed will redevelop within 12 months. Because cancerous mammary tumors are so aggressive in cats, their overall prognosis is guarded, especially since these tumors metastasize.