Mammary tumors are among the most common tumors in the cat; Domestic Shorthairs and Siamese may have higher incidence rates than other breeds. The mean age at presentation is 10 to 12 years. Most affected cats are intact females; however, the disease is occasionally seen in spayed females and, rarely, in male cats. Several reports have documented a strong association between the use of contraceptives and the development of benign or malignant mammary masses in cats.
Approximately 85% of feline mammary tumors are malignant, and are histologically classified as adenocarcinomas. Sarcomas, mucinous carcinomas, duct papillomas, adenosquamous carcinomas, and adenomas are rarely seen. The benign mammary gland dysplasias (lobular hyperplasia and fibroepithelial hyperplasia) are less common.
Before any diagnostic or therapeutic steps are taken, the health status of the cat must be fully assessed. Bloodwork and urinalysis should be done to identify any presurgical abnormalities. Thoracic radiographs (both right and left lateral and ventrodorsal planes) should be obtained to search for pulmonary, lymph node, and pleural metastases. A preliminary biopsy is usually not recommended because 80 to 85% of the masses in the mammary gland of cats are malignant. Regional lymph nodes (lymph glands) should be palpated carefully; fine-needle aspiration or surgical removal are necessary to determine the presence of metastases.
Surgery is the most widely used treatment for mammary neoplasms in the cat; it is used alone or in combination with chemotherapy. Radical mastectomy (i.e., removal of all glands on the affected side) is the surgical method of choice because it significantly reduces the chance of local tumor recurrence. As opposed to the dog, in which more conservative resections may be appropriate in carefully selected cases, most cats benefit from a complete unilateral or bilateral mastectomy. The inguinal lymph node is virtually always removed with the mammary gland, while the axillary lymph nodes are removed only if enlarged and cytologically positive for tumor.
Combination chemotherapy using doxorubicin and cyclophosphamide or carboplatin has been shown to induce short-term responses in about half of the cats with metastatic or nonresectable local disease, and is recommended after complete excision of the tumor to prolong disease-free period of and to delay the development of metastases. This chemotherapeutic drugs are given every 3 to 4 weeks for 4 to 6 cycles after complete removal of the primary tumor. Side effects associated to these protocols are anorexia (lack of appetite) and myelosuppression (low blood counts).
With conservative surgery, 66% of the cats have a recurrence at the surgical site. The most significant prognostic factors affecting recurrence and survival times for cats with malignant mammary tumors are tumor size, extent of surgery, and histologic grading. Tumor size is the single most important prognostic factor. Cats with tumors larger than 3 cm in diameter have a median survival time of 4 to 6 months; cats with tumors 2 to 3 cm in diameter have a median survival time of about 2 years, and cats with tumors less than a 2 cm in diameter tumor have a median survival time of over 3 years.
Thus, early diagnosis and treatment is vital in cats with mammary tumors.