Mairin Miller, DVM.

Practice Limited to Oncology
Veterinary Specialty Hospital – North County

80-95% of mammary tumors in the cat are malignant. While older cats and the Siamese breed are more likely to develop mammary tumors, the most influential factor for the development of mammary cancer in cats is exposure to ovarian hormones. Cats spayed before 6 months of age have a 91% decreased risk and cats spayed prior to 1 year of age have an 86% decreased risk of developing mammary tumors compared to intact female cats.

Since the majority of mammary tumors in cats are malignant, further diagnostics to look for spread of disease is recommended prior to surgery. Mammary tumors most commonly will spread to the local lymph nodes and lungs. Chest x-rays and an abdominal ultrasound are recommended to look for cancer spread. Full blood work and a urinalysis are recommended to look for any other underlying disease processes or organ dysfunction.

Three factors have been consistently found to affect prognosis: size, lymph node metastasis, and grade. Cats with low grade tumors that are less than 2 cm in size, and haven’t metastasized have a better prognosis than cats with high grade tumors, larger tumors and/or those with metastatic disease. Survival times can range from 6 months to 2-3 years depending on these factors and the treatment performed.

As these cats can go on to develop more mammary tumors, it is recommended to perform a full-chain mastectomy of at least the affected mammary chain, and often both mammary chains. Bilateral chain mastectomies are commonly performed as staged procedures 4-6 weeks apart and according to recent literature may improve prognosis.

Due to the aggressive nature of feline mammary carcinomas, post-operative chemotherapy is often recommended. Most commonly a drug called doxorubicin is utilized, however other drugs such as mitoxantrone and carboplatin have been investigated as well. Chemotherapy is usually initiated once the incision has healed.

Overall, feline mammary tumors have an aggressive behavior, with a high rate of malignancy and a significant potential to metastasize, most frequently to the lymph nodes and lungs. Early detection and aggressive treatment with radical surgery and adjuvant chemotherapy, however, can improve prognosis. Most importantly, though, spaying cats prior to their first estrus cycle is the most effective way of reducing the risk of mammary tumor development.

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