Pathology and microbiology of dermal squamous cell carcinoma in young brown chickens reared on reused litter.

Dermal squamous cell carcinoma (DSCC) was found in young brown chicken flocks reared on reused litter in Japan. DSCC was often detected at slaughter from April 2007 to March 2009, especially in June and July 2007. No DSCC was observed in the broiler chickens on the farms. Twelve 11-wk-old brown chickens with DSCC were investigated pathologically and microbiologically. Various degrees of crater-like skin lesions were found on the back, waist, neck, legs, abdomen, and wings of the carcasses. The feather follicles were enlarged. The feather follicular epithelial cells proliferated, and the squamous cells proliferated neoplastically in association with collagen fibers and fibroblasts in the dermis under the feather follicular epithelium. "Keratin pearl" structures were often seen in the dermis. Immunohistochemically, the keratin antigen was positive in the neoplastically proliferated squamous cells in the dermis. Avian leukosis virus antigens could not be found in the neoplastic squamous cells in the dermis. Ultrastructurally, no viral agents could be detected in the skin with DSCC. Virologically, reverse transcription-polymerase chain reactions of the skin with DSCC for fowlpox virus and avian leukosis virus were negative. No viruses could be isolated from the skin with DSCC. This study suggests that the chicken breed, reused litter, and season may be associated with the incidence of DSCC in brown chickens.