Domestic Shorthair Case

Species: Feline
Breed: Domestic Shorthair
Age: 3Y
Gender: Female, Spayed



SOURCE/HISTORY  :2 cm mammary mass on left central mammary gland.

Click here for the IDEXX Pathology Report on this case.


The specimen is characterized by a moderately well demarcated and partially encapsulated proliferation of atypical mammary gland epithelium. These cells are proliferating as tortuous and rudimentary ductular elements. Individual cells are characterized by a cuboidal appearance with a moderate amount of eosinophilic cytoplasm and moderately pleomorphic euchromatic nuclei and variably sized nucleoli. There are 5 mitotic figures per 10 high power fields. There is necrosis of the center of the mass with abundant cellular detritus present. Small aggregates of lymphocytes and plasma cells are present at the periphery of the mass. Excision is complete. The lateral margin and deep margins measure less than 0.5 mm. Vascular invasion is not observed.


Haired skin: Mammary adenocarcinoma

Mitotic index: 5 (5 mitotic figures per 10 high power fields)

Excision: Complete, lateral margin and deep margins measure less than 0.5 mm.

Vascular invasion: Not observed


Mammary tumors are the third most common tumor in the cat, after hematopoietic neoplasms and skin tumors. The incidence of mammary tumors in the cat is less than half that seen in dogs; however, these tumors account for 17% of neoplasms in female cats. Mammary tumors also occur in male cats, although infrequently. At least 85% of feline mammary tumors are malignant. Some evidence suggests breed associated predilection for mammary tumors. Domestic Shorthair and Siamese cats appear to have a higher incidence. Siamese cats may have twice the risk of developing mammary tumors than any other breed. Mammary neoplasia has been reported in cats from 9 months to 23 years of age. Hormonal influences probably are involved in the pathogenesis of mammary tumors in the cat. Cats spayed at 6 months of age had an approximately sevenfold reduced risk of mammary cancer than intact cats. A strong association also has been documented between previous administration of drugs containing synthetic progestins or estrogen progestin combinations and development of benign or malignant mammary tumors in cats. In both cases, the risk was more than threefold greater than that of untreated cats.

Between 85% and 93% of feline mammary tumors are histologically malignant. Most tumors are estrogen receptor negative. Many of the tumors, especially the large, more invasive neoplasms, adhere to the skin and are ulcerated. Lymphatic invasion and lymph node metastasis are common. In several studies, more than 80% of cats with mammary malignancy had metastases to one or more of the following organs at the time of death: lymph nodes, lungs, pleura, liver, diaphragm, adrenal glands, and kidneys. More than 80% of feline mammary tumors are classified histologically as adenocarcinomas. Development of additional mammary tumors is common. There is a better prognosis associated with early removal of small masses. J Feline Med Surg. 2013; Vet J. 2012 Oct.; 194(1):19-26.


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