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Mammary (Breast) Tumors in Cats

By Cheri A. Johnson, DVM, MS, DACVIM (Small Animal), Professor, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University
James A. Flanders, DVM, DACVS, Associate Professor, College of Veterinary Medicine, Cornell University
Autumn P. Davidson, DVM, MS, DACVIM, Clinical Professor, School of Veterinary Medicine, University of California, Davis
Fabio Del Piero, DVM, DACVP, PhD, Professor, Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University
Mushtaq A. Memon, BVSc, PhD, DACT, Theriogenologist, Department of Veterinary Clinical Sciences, Washington State University
Robert C. Rosenthal, DVM, PhD, DACVIM (Small Animal, Oncology), DACVR (Radiation Oncology),
Brad E. Seguin, DVM, MS, PhD DACT, Professor Emeritus, Department of Clinical and Population Sciences, College of Veterinary Medicine, University of Minnesota

Also see professional content regarding mammary tumors.

The frequency of mammary tumors in different species varies tremendously. They are relatively common in cats. Approximately 90% of mammary tumors in cats are malignant (cancerous). The cause of mammary tumors is unknown, however hormones play an important role in their development. Mammary tumors in cats are most often seen in older (average age 11 years) nonspayed females. Spaying at a young age reduces the risk, but the degree of protection is less precisely documented than that for dogs. Breast tumors are diagnosed by physical examination, x‑rays, and tissue samples (biopsy). They often spread to the lungs, so chest x-rays are also taken to check for that possibility. Treatment includes removal of the tumor or the entire breast and anticancer drug treatment. The outlook is worse in cats with larger tumors and those with a high grade of malignancy, as determined by the biopsy.