AVIAN KERATOACANTHOMA (DERMAL SQUAMOUS-CELL CARCINOMA) IN BROILER CHICKEN CARCASSES

Multiple lesions of dermal squamous cell carcinoma are found at a low frequency (0.04%) in the carcasses of young meat-type chickens at slau ghter. For this study, affected carcasses (n = 308) were removed from the processing line, and lesions were characterized by size, distribut ion, and morphology. Carcasses were also sexed and examined for eviden ce of metastasis. Nodular (n = 297) and ulcerative (n = 1,707) lesions were counted and examined. Most lesions were present in the pectoral, dorsopelvic, and femoral feather tracts. Few lesions (n = 11) were fo und in wing tracts. Mean diameter was 5.4 mm for ulcerative lesions an d 3.1 mm for nodular lesions. Histologic sections of ulcerative (n = 5 79) and nodular (n = 113) lesions were examined. Small nodular lesions originated from hyperplastic feather follicle epithelium. Nodules con tained keratin-filled cysts lined by squamous epithelium that were ass ociated with isolated islands and infiltrating cords of dermal keratin ocytes. Loss of surface epithelium resulted in noduloulcerative and ul cerative lesions. Invasion of underlying skeletal muscle and evidence of visceral metastasis were not present, but invasion through elastic laminae and into the subcutis was present in 20.5% (134/654) of the le sions examined. The nodular lesions in these carcasses were morphologi cally similar to early nodular lesions previously described in live ch ickens as avian keratoacanthomas. A retrospective study compared selec ted production parameters and disease condemnations to the prevalence of squamous cell carcinoma in 665 flocks of broiler chickens. There wa s a positive correlation (P < 0.0001) with the occurrence of airsaccul itis but a negative correlation with increased age and condemnations f or leukosis (P < 0.0001). Tumor frequency followed a pronounced season al pattern, with decreased prevalence in summer months.