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.