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 i ncidence of mammary gland cancer in zoo felids in which progestin cont raception has been used. Our purpose was to describe the clinical beha vior of these tumors and identify risk factors for their development. Clinical and historic records were reviewed from 31 captive wild felid s with palpable and histologically confirmed mammary gland neoplasia. All mammary masses were classified histopathologically as carcinomas, with cribiform, solid, cyst-papillary, and adenocarcinoma patterns. Th oracic radiography was a sensitive antemortem procedure to detect meta stases. Although other abnormalities (anorexia/lethargy, ventral mass or ulcer visible, anemia, neutrophilia, hypercalcemia or azotemia) wer e noted, concurrent geriatric diseases often confounded clinical inter pretation. Therefore, these findings were not specific for a diagnosis of cancer. Metastases were most common in lymph node, lune, and liver . Mammary cancer was most common in animals that had been implanted wi th 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 ((x) over bar +/- SD = 13.87 +/- 2.60 yr) versus n ontreated felids (16.33 +/- 0.94 yr). Mammary cancer behaves as aggres sively in wild felids as in domestic cats, and long-term exogenous pro gestin exposure is a risk factor in its development. Zoos using MGA in felids should be cognizant of the strong association between progesti n exposure and mammary cancer development and should employ alternativ e contraceptive methods whenever possible.