Mammary cancer in captive wild felids and risk factors for its development: A retrospective study of the clinical behavior of 31 cases

This retrospective: study was initiated because of the perceived high incidence of mammary gland cancer in zoo felids in which progestin contraception has been used. Our purpose was to describe the clinical behavior of these tumors and identify risk factors for their development. Clinical and historic records were reviewed from 31 captive wild felids with palpable and histologically confirmed mammary gland neoplasia. All mammary masses were classified histopathologically as carcinomas, with cribiform, solid, cyst-papillary, and adenocarcinoma patterns. Thoracic radiography was a sensitive antemortem procedure to detect metastases. Although other abnormalities (anorexia/lethargy, ventral mass or ulcer visible, anemia, neutrophilia, hypercalcemia, or azotemia) were noted, concurrent geriatric diseases often confounded clinical interpretation. Therefore, these findings were not specific for a diagnosis of cancer. Metastases were most common in lymph node, lung, and liver. Mammary cancer was most common in animals that had been implanted with melengestrol acetate (MGA)-impregnated silastic devices (n = 29, 94%). This association was statistically significant (P < 0.002). There was no significant difference in age at diagnosis of mammary cancer in MGA-treated felids (x̄ ± SD = 13.87 ± 2.60 yr) versus nontreated felids (16.33 ± 0.94 yr). Mammary cancer behaves as aggressively in wild felids as in domestic cats, and long-term exogenous progestin exposure is a risk factor in its development. Zoos using MGA in felids should be cognizant of the strong association between progestin exposure and mammary cancer development and should employ alternative contraceptive methods whenever possible.