JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2026123): A cat
HISTORY: This cat had diffusely swollen and enlarged mammary glands along the entire mammary chain.
HISTOPATHOLOGIC DESCRIPTION: Mammary gland: Diffusely, the mammary gland is expanded by variably sized lobules composed of hyperplastic ducts surrounded by multiple layers of myofibroblasts imbedded within an loose stroma that blends into dense bands of collagenous stroma. Ducts are lined by 1-3 layers of cuboidal to columnar epithelial cells. The surrounding spindle cells (myoepithelial cells) have indistinct cell borders, a scant amount of eosinophilic fibrillar cytoplasm, an oval nucleus with finely stippled chromatin, and 1-2 nucleoli. Multifocally ducts are filled with small amounts of necrotic debris, sloughed epithelial cells, and few neutrophils. Within the periductal stroma there are moderate numbers of foamy macrophages and fewer lymphocytes and plasma cells. Diffusely the superficial dermis is mildly expanded by increased clear space and ectatic lymphatics (edema). The epidermis is mildly hyperkeratotic.
MORPHOLOGIC DIAGNOSIS: 1. Mammary gland: Hyperplasia, fibroepithelial, diffuse, moderate, breed unspecified cat, feline.
CAUSE: Prolonged elevated levels of progesterone
CONDITION: Mammary fibroadenomatous hyperplasia
SYNONYMS: Fibroepithelial hyperplasia, feline mammary hypertrophy
- Benign, nonneoplastic proliferation of mammary ducts and connective tissue of young intact female cats (<2yrs old), pregnant cats, or older neutered male and female cats on prolonged progesterone therapy (megestrol acetate)
- Regression following ovariohysterectomy or termination of pregnancy or progesterone therapy
- Coincides with the luteal phase of estrus, early in pregnancy, or after progestin therapy
The mechanism for progesterone induced hyperplasia involves IGF-1 and growth hormone
- Prolonged exposure to endogenous or exogenous progesterone
- Exact mechanism unknown
TYPICAL CLINICAL FINDINGS:
- Sudden rapid uniform enlargement of one or more mammary glands
- Firm and painless, unless ulcerated
TYPICAL GROSS FINDINGS:
- One or all mammary glands markedly enlarged
- Overlying skin: Pink to blue, +/- necrosis
- Cut surface: White to pink, bulges, multinodular with blue fibrous septa forming a reticulated pattern, edema, hemorrhage, necrosis
- Intraductal pattern: Project from wall of fluid‑filled space as a polypoid or dome shaped mass or more annular growth around a central cavity
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Unencapsulated mass composed of lobules of branching ductal structures lined by epithelial cells surrounded by edematous myofibroblastic stroma
- Duct-like structures lined by several layers of cuboidal to columnar epithelial cells with vesiculate nuclei
- Mitoses may be common in both ductal and myofibroblast populations
- Neoplasia: Usually does not involve all glands; usually a discrete nodule; epithelial component disorganized and/or invasive
- Other non-neoplastic mammary gland proliferations
- Cystic dilation of mammary ducts: due to obstruction of duct leading to dilation; common in dogs and cats
- Mammary hypertrophy: generalized hyperplasia of all mammary tissue
- Galactostasis: engorged, hot, painful mammae secondary to milk retention (failure of let-down d/t inhibition of oxytocin release)
- Rats: Mammary gland benign fibroadenomas; elevated prolactin; common in older female Sprague-Dawley rats
- Rabbits: Mammary hyperplasia can be caused by the administration of cyclosporine
- Water Buffalo: Mammary gland fibroadenomatoid hyperplasia; probable hormone influence
- Barthold SW, Griffey SM, Percy DH. Pathology of laboratory rodents and rabbits. 4th ed. Ames, IA: John Wiley & Sons, Inc.; 2016:164-166.
- Foster RA. Female reproductive system and mammae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:1193.
- Goldschmidt MH, Pena L, Zappulli V. Tumors of the mammary gland. In: Meuten DJ, ed. Tumors in domestic animals. 5th ed. Ames, IA: John Wiley & Sons, Inc.; 2017:758.
- Krimer PM, Harvey SB, Blas-Machado U, Lauderdale JD, Moore PA. Reversible fibroadenomatous mammary hyperplasia in male and female New Zealand white rabbits associated with cyclosporine A administration. Vet Pathol. 2009;46:1144-1148.
- de Sant’Ana FJF, Carvalho FC et al. Mammary diffuse fibroadenomatoid hyperplasia in water buffalo (Bubalus bubalis): three cases. J Vet Diagn Invest. 2014 May 12;26(3): 453-456.
- Schlafer DH, Foster RA. Female genital system. In: Maxie MG, ed. Pathology of Domestic Animals. Vol 3. 6th ed. St. Louis, MO: Elsevier; 2016:460-461.