A young neutered male cat presented several times for dermatopathy. On the first presentation, a pruritic, hemorrhagic lesion was found on the chin. The cat was treated with topical cleansing, antibiotics, and oral prednisone. One month later, the cat returned with chin lesions, which remained pruritic, as well as two additional lesions. The owners declined biopsy. An eosinophil-granuloma complex was suspected, and methylprednisolone acetate (4 mg/kg SQ) was administered. A hypoallergenic food trial was begun. The cat presented 38 days after the initial presentation with continuing pruritus. The therapeutic regimen was modified at this time to include oral megestrol acetate. The cat received 1 mg/kg daily for 2 days and then 0.5 mg/kg daily for 16 days. The cat was scheduled for a recheck 58 days after initiation of megestrol acetate treatment. At that time, it had an acute mammary enlargement and was reluctant to walk. The most severely affected gland was the right inguinal, but all six mammary glands were asymmetrically enlarged. Because of the recent history of progestin treatment, mammary hyperplasia was considered the most likely diagnosis. Other causes could have been mammary adenocarcinoma or carcinoma, mammary adenoma, or mammary sarcoma. The histologic diagnosis was mammary fibroadenomatous hyperplasia. The presence of neutrophils under an ulcerated area suggested superficial mastitis.

Therapy with megestrol acetate has been associated with mammary fibroepithelial hyperplasia. Mammary fibroadenomatous hyperplasia is a rather uncommon sequela but should be considered when using this progestin for therapy. It is possible that there was synergistic action between the exogenous methylprednisolone acetate given 3 days before and the megestrol acetate.

Mammary fibroadenomatous hyperplasia in a young cat attributed to treatment with megestrol acetate. MacDougall LD. CAN VET J 44:227-229, 2003.