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Mammary Hypertrophy in Cats

(Fibroadenoma Complex, Mammary Fibroadenomatosis, Glandular Mammary Hypertrophy)


Clare M. Scully

, MA, DVM, MS, DACT, Louisiana State University, Department of Veterinary Clinical Sciences

Reviewed/Revised Jul 2023
Topic Resources

Feline mammary hyperplasia is a benign, progesterone-associated fibroglandular proliferation of one or more mammary glands that may occur in both the female and male cat. This condition is usually seen in young sexually intact females following estrus, and in male and female cats receiving long-term treatment with progestogens.

Etiology of Mammary Hypertrophy in Cats

There are two types of feline mammary hyperplasia described: lobular hyperplasia and fibroepithelial hyperplasia.

Epidemiology of Mammary Hypertrophy in Cats

There is no breed disposition. Feline mammary hyperplasia can occur in young, cycling, or pregnant cats; aged, sexually intact females and males; and neutered males after treatment with progestins.

Clinical Signs of Mammary Hypertrophy in Cats

The clinical finding characteristic of mammary hypertrophy in cats is palpable masses in one or more mammary glands in a sexually intact cat 1–14 years old. The onset of swollen mammary glands is acute.

The size of the enlarged glands is quite variable, ranging from 1.5 to 18 cm. In chronic situations, ulceration of the mammary glands due to enlargement, skin necrosis, and trauma may be noted. No milk is produced in the diseased glands in pregnant animals.

Diagnosis of Mammary Hypertrophy in Cats

Diagnosis of feline mammary hyperplasia is made based on signalment, clinical signs, and history. Histologically, no inflammation or necrosis is noted.

Although a benign condition in cats, biopsy is indicated. Given that 80% of mammary tumors in cats are malignant, any mammary mass in cats has to be addressed with concern.

Differential diagnoses include:

  • acute mastitis

  • mammary tumors (mammary adenocarcinoma, mammary carcinoma, mammary adenoma, mammary sarcoma)

Treatment of Mammary Hypertrophy in Cats

Feline mammary hyperplasia may spontaneously regress if left untreated.

Treatment of feline mammary hyperplasia involves removal of the progesterone source. This can be through one of the following means:

  • Administration of antiprogestins

  • Ovariectomy or ovariohysterectomy for animals in diestrus

  • Mastectomy in animals not responding to other surgical or medical treatments

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