Zoological Pathology Program, Loyola University Medical Center, University of Illinois, Maywood, IL, USA
A high incidence of urinary bladder transitional cell carcinoma (TCC) has been noted in captive fishing cats (Prionailurus viverrinus), small primarily piscivorous felids native to Southeast Asia and Indonesia.8 Of the 91 adult (>1 yr) deaths between 1995 and 2004, 12 (13%) were attributed to TCC.4,11 In contrast, the incidence of urinary TCC in domestic cats is <1%.3,9
To help elucidate possible mechanisms for bladder carcinogenesis in fishing cats, archival sections of urinary bladder from 12 fishing cats were examined histologically and by immunohistochemistry for expression of p53, cyclooxygenase (COX)-1, and COX-2. Eight cats had TCC and four were unaffected. Affected fishing cats (5.3) were all captive-born with an average age of 10.8 yr (range 7.5–16 yr). Unaffected cats were all captive-born, males with an average age of 10.5 yr (range 8–13.5 yr).
The majority of fishing cat TCCs (7/8) were histologically characterized by extensive mural infiltration. A subset of these tumors (4/7) also had luminal papillary components. A single case consisted of carcinoma in situ. Squamous metaplasia, necrosis, and lymphatic invasion were prominent features in most tumors. Metastasis was documented in two individuals.
p53, a gene involved in control of the cell cycle and apoptosis, is frequently mutated in human cases of TCC.10 In the fishing cats, only 2/8 TCCs had significant positive immunoreactivity for p53. In the remaining six tumors, positive staining was detected in rare, widely scattered cells, comparable to that noted in sections of normal bladder. Therefore, mutation of the p53 gene did not appear to be an essential component of bladder carcinogenesis in fishing cats.
Cyclooxygenase enzymes are involved in the production of prostaglandins.5 The COX-2 isoform is induced by a variety of inflammatory mediators5 and overexpression has been detected in several types of epithelial neoplasms1,2,6,7. COX-2 immunoreactivity was detected in all eight TCCs with staining limited to the infiltrative portions of the tumors. In contrast, only 1/4 normal bladders had rare individual immunoreactive cells. COX-1 immunohistochemistry was uniformly negative in all eight tumors. COX-2 overexpression suggested that prostaglandin-mediated mechanisms of carcinogenesis are important in this species and treatment with cyclooxygenase-inhibiting, nonsteroidal anti-inflammatory drugs (NSAIDs) could be of therapeutic benefit.
We would like to thank Stacy Schultz, Jane Chladny, and the University of Illinois histology laboratory for technical assistance and slide preparation. We’d also like to thank Dr. Bill Swanson and Linda Curtis for providing the Fishing Cat International Studbook and helping to identify the fishing cat TCC cases. Finally, we’d like to acknowledge the veterinarians and staff at the San Diego Zoo and Wild Animal Park, Cincinnati Zoo and Botanical Gardens, Memphis Zoo, Capron Park Zoo, and Audubon Zoo for their contributions of case materials.
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