Feline mammary tumours
- Around 80-90 percent mammary gland tumours in cats are malignant (serious).
- Size of the tumour is probably the best prognostic indicator, whereas factors like age of the patient, tumour number and location have less prognostic value.
- Tumour size larger than two cm is considered to be serious.
- Risk of feline mammary tumours is similar for spayed and non-spayed cats.
- Chemotherapy may have minimal anti-tumour activity. But adjunct chemotherapy may be used together with surgery to remove the tumours.
Mammary neoplasms in the cat have been treated in a variety of ways. Surgery is the most widely used treatment. It may be used alone or in combination with chemotherapy or other modes of cancer therapy.
The success of surgery is hindered by the invasive nature of the disease and its tendency for early metastasis. 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 tumour recurrence. This procedure is frequently utilised, regardless of the size of the tumour.
The surgeon’s knowledge of the anatomy of the area is critical for local control of the tumour. The cat, unlike the dog, usually has four pairs of mammary glands. The two cranial glands on each side have a common lymphatic system and drain into the axillary lymph nodes and then to sternal nodes. The two caudal glands tend to drain to inguinal lymph nodes.
Several surgical principles are observed when performing a mastectomy on feline mammary tumour patients. As opposed to the dog, in which more conservative resections may be appropriate in carefully selected cases, most cats require a complete unilateral or bilateral mastectomy. Tumour fixation to the skin or abdominal fascia necessitates en bloc removal of these structures. Complete unilateral mastectomy is usually performed if the tumours are confined to one side. Staged mastectomy (two weeks apart) or simultaneous bilateral mastectomy is done when the tumours are bilateral. The inguinal lymph node is virtually always removed with gland, while the axillary lymph nodes are removed only if enlarged and cytologically positive for tumour. Aggressive or prophylactic removal of axillary nodes, whether positive or negative, probably has little therapeutic benefit.
Although ovariohysterectorny has been shown not to decrease the incidence of recurrence, some believe that it is warranted because of the occasionally seen coexisting ovarian and uterine disease. If the mammary mass is due to a benign condition such as fibroepithelial hyperplasia, ovariohysterectorny often results in regression of the hyperplastic tissue. This condition often resolves spontaneously within a few weeks of diagnosis; in some cases, without performing an ovariohysterectorny.
Radiation therapy is not used routinely to treat feline mammary tumours. Currently, there are no major claims that radiation increases the survival rate of feline mammary tumour patients.
Combination chemotherapy has been shown to induce short-term responses in about half of the cats with metastatic or nonresectable local disease. In one study, 7 of 14 (50 percent) had a partial response (>50 percent regression). The chemotherapy protocol can be repeated every 3 to 4 weeks. We have found that the major side effect with this protocol has been profound anorexia and mild myelosuppression. Reducing the dose may limit toxicity to an acceptable level. Prospective studies using combined adjuvant chemotherapy and mastectomy in the cat have yet to be performed.
(Dr M Chandrasekar is Associate Professor at the Department of Veterinary Medicine, Ethics and Jurisprudence, Madras Veterinary College, Chennai).