Mammary gland masses from an approximately 7-month-old cat were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for histopathology. The cat was reported to have multiple mammary gland masses ranging from marble-sized to 6 cm wide. These masses had acute, rapid development and had doubled in size over a 2-week period. The cat was spayed at the time of surgical mass removal.
Histologically, the submitted masses consisted of proliferating mammary gland ducts surrounded by dense mesenchymal tissue (Figure 1). Findings were consistent with mammary gland fibroadenomatous hyperplasia. Fibroadenomatous hyperplasia, also known as fibroadenomatous change or fibroepithelial hyperplasia, is a non-neoplastic, benign condition that is seen most often in young, intact female cats. This lesion is associated with prolonged progesterone or other hormonal exposure, via endogenous or exogenous sources. It typically affects all mammary glands and, in some cases, the enlarged glands can become ulcerated and secondarily infected. This condition can sometimes mimic neoplasia, though the young age of the patient, if known, should be used to heighten suspicion for hyperplasia. This condition is often cured with removal of the progesterone source, which is most commonly achieved with ovariohysterectomy.
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