Feline Mammary Tumors

Veterinary Hospital of the University of Pennsylvania
Last Modified: November 1, 2001

Mammary cancer is the third most common cancer in cats. The average age of affected cats is 10-11 years of age. Almost 90% of feline mammary tumors are malignant, meaning they have the potential to spread to other portions of the body. The most common sites of spread are regional lymph nodes and the lungs. Malignant mammary tumors in cats tend to metastasize rapidly. Around 10% of feline mammary tumors are benign, meaning they will not spread except by local growth. To date, surgical excision at the earliest possible opportunity is the most effective therapy for any mammary tumor. If the tumor is benign, complete surgical excision is curative. If the tumor is malignant, post-surgical treatment with chemotherapy, immunotherapy or radiation therapy may be warranted. These options will be discussed with you by the medical oncologist following surgery, if appropriate.

Spaying at the time of mammary tumor resection has no measurable effect on the rate of tumor reoccurrence. It is unclear whether spaying a cat early in life diminishes the risk for development of mammary cancer later on.

Biopsying mammary tumors prior to removing them is not recommended for the following reasons:

initially benign tumors may transform at a later date to malignant forms.
multiple tumors must be individually biopsied, as each may well be a different subtype of mammary tumor.
within the same mass, a mixture of benign and malignant tissue may be present.

Instead, we recommend a single surgical procedure in which all affected tissue or potentially affected tissue is excised.

The recommended surgical treatment for feline mammary tumors is the radical mastectomy. In this procedure, all four mammary glands on the affect side plus the axillary (arm-pit) lymph node and the inguinal (groin) lymph node are removed. Whem mammary glands on both left and right chains are affected, two separate radical mastectomies done four weeks apart are required.

The suture line following a radical mastectomy extends from the axilla to the vulva. On occasion, small rubber drains will be inserted in the inquinal region to prevent fluid accumulation. These drains are removed 3-4 days after surgery. All cats are bandaged after surgery. These bandages are usually removed 3-4 days after surgery. Some cats then require an elizabethan collar to discourage them from chewing at the sutures.

The cat's activity must be curtailed post-surgically to avoid fluid build up along the suture line or dehiscence (wound gaping). Climbing stairs, jumping from furniture and energetic play should be discouraged. Pathologic diagnosis of the tumor will be available 5-7 days after surgery and we will telephone you with these results. Ten to fourteen days after surgery, the sutures will be removed.