Feline Medicine Q&A 18

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A 3-year-old neutered female cat presents with firm non-painful roughly symmetrical swelling of the mammary glands. The cat is systemically well and showing no other signs.

Question	Answer		Article
What is the likely cause of the swelling and how can the diagnosis be confirmed?	This is most likely to be a case of mammary hyperplasia (fibroadenomatous/fibroepithelial hyperplasia). It occurs in both male and female cats, but is more common in the latter. There is usually a very marked increase in the size of one or, more usually, multiple mammary glands. The swelling can get to such a size that it causes overlying cutaneous ulceration. The diagnosis is confirmed by biopsy and this differentiates it from other conditions such as neoplasia and mastitis.		Link to Article
What is known about the cause(s) of this disease, and how can such cases be managed?	Most affected cats are young entire females, and it is assumed that the hyperplasia develops in response to excessive progesterone production (although serum concentrations are not necessarily abnormal). In other cats, there is a history of exogenous progestagen use (oral, or depo-injectable drugs) which has been clearly linked to mammary fibroepithelial hyperplasia in cats. In a small proportion of cases, the disease occurs in neutered females or male cats with no exogenous progestagens having been administered. It is not clear if these cats also have excessive endogenous progesterone from another source. Spontaneous resolution of the condition typically (but not always) follows removal of the presumed source of progesterone (withdrawing drug therapy, neutering an entire female) but this can be very slow. If response is inadequate, or if there is not an obvious source of progestagens, administration of the progesterone receptor antagonist, aglepristone, has recently been reported to be highly successful. Doses used have been 10 mg/kg SC twice weekly or 20 mg/kg SC once weekly for 1–4 weeks, or 10 mg/kg SC daily for 4–5 days.		Link to Article