Mammary Gland Tumor in Cats

Nearly one third of all tumors in cats occur in the mammary, or breast, area of female cats. Mammary gland tumors are typically malignant, meaning cancerous, and rapidly metastasize, or spread to nearby lymph nodes or other areas of your cat’s body. Some studies have shown that over 85 percent of mammary tumors in cats are cancerous, making for a high likelihood that a mammary gland tumor on your cat will be a life-threatening situation. Of these cancerous tumors, the majority are adenocarcinomas, a type of cancer that affects the epithelial cells located under the outer layer of breast tissue. Given the fast rate of growth and spread of these tumors, veterinary care should be sought quickly for the best possible outcome. 

Initially, the mammary gland tumor in your cat will have few, if any, symptoms. It is only as the tumor begins to grow that your cat will experience any pain or discomfort. Things you should watch for include:

• Bumps or masses underneath the skin in the mammary or breast area
• Ulceration, or weeping wound that will not heal, in the breast area
• Lack of appetite as the disease progresses and the cancer spreads to other systems
• Eventually, depression or lethargy as the cancer spreads

As with many cancers, the exact cause of mammary gland tumors in cats are unknown. Some of the typical suspected causes of cancer, such as environmental factors or exposure to known carcinogenic chemicals, have not been shown to have a direct correlation with mammary gland tumors. The largest connection to mammary gland tumors has been the presence of sex hormones. Studies have found that cats that have been spayed before a year of age are 86 percent less likely to develop cancerous mammary tumors during their life. 

Diagnosis of mammary gland tumors in your cat will begin with a thorough physical examination by an experienced veterinarian. Your vet will gently feel the mammary/belly area of your cat to determine the size and location of any mammary gland tumors. Your vet will also gently palpate the lymph nodes located in the mammary area to determine whether they are inflamed. Inflamed lymph nodes in the mammary area could indicate that the cancer has begun to metastasize.

Your veterinarian will also order x-rays for your cat. X-rays will be used to identify the precise location of the tumor and its approximate size. X-rays of the chest and head area can also show if the cancer has begun to spread to other parts of the body, which can help determine which course of treatment would be the most appropriate for your cat. A fine needle biopsy, in which a needle is inserted into the tumor to extract cells, is sometimes used to definitively diagnose cancerous tumors. However, given the high percentage of tumors that are cancerous, your vet may choose to skip this test and proceed straight to treatment.

Treatment of mammary gland tumors in your cats will take one of two forms; surgery or chemotherapy.

Surgical Treatment

Surgery is the preferred method of treatment of mammary gland tumors. Your veterinarian will first perform pre-surgical x-rays in order to determine the approximate size and location of the tumor. This will also allow your vet to determine whether the cancer has spread to the lymph nodes or vital organs. As with any major surgery, your vet will also order a full blood panel to determine if there are any additional underlying conditions that may create additional risk during anesthesia or surgery.

During the surgery, your vet will either remove the tumor or opt to perform a complete mastectomy. Both procedures carry a similar degree of risk and the mastectomy reduces the chance that tumors will regrow or that additional tumors will form. Your vet may also choose to remove the lymph nodes that are located in the mammary area at this time.

Chemotherapy Treatment

The other treatment option for mammary gland tumors is chemotherapy. Chemotherapy is used either alone or in connection with surgical treatment. During chemo, your cat will be prescribed a series of medications administered at regular times. These medications can slow the growth of tumors and can kill any remnant cancer cells or tissue that may not have been operable. Chemotherapy has serious side effects such as lethargy, depression, and lack of appetite. Some of these side effects can be minimized through the use of other medications.

For recovery from surgery, you will need to carefully follow all post-surgical instructions, including follow up visits for suture or staple removal. With either chemotherapy or surgery your vet will recommend regular follow-up exams to ensure that the cancer has not returned or spread.

The prognosis for your cat will often depend on the size of the tumor. Because mammary gland tumors grow and metastasize quickly, the sooner the condition has been identified and treated the lesser the chances are that the cancer has spread to other parts of your cat’s system. In cats treated with surgery and with relatively small tumors, the average life expectancy is increased up to six years. As the tumor size grow, the prognosis for full recovery lessens. In cases of the largest tumors, or when the cancer has begun to metastasize, surgery has been shown to extend life expectancy three to six months.