Spontaneous squamous carcinoma of the esophagus in chickens.

Histologic preparations from 149 gullets from chickens from the Linxian county (Henan province, northern China) having intraepithelial neoplasms or invasive carcinomas were reviewed. Invasive squamous cell carcinomas were found in 134 animals and invasive adenocarcinomas in seven. The remaining eight specimens had only intraepithelial neoplastic lesions: four with low-grade dysplasia and four with high-grade dysplasia (one with carcinoma in situ). The degree of differentiation in invading tumors was as follows: of the 134 invasive squamous carcinomas, two were highly differentiated, 125 moderately differentiated, and 22 poorly differentiated. All seven adenocarcinomas were moderately differentiated. In 97 of the 149 invasive carcinomas, intraepithelial neoplastic lesions were observed near the tumors: in 96 adjacent to invasive squamous carcinoma, and in one in the glandular epithelium adjacent to invasive adenocarcinoma. In the remaining 44, only invasive carcinoma was present. Epithelial buds bulging into the stroma were present in intraepithelial neoplastic lesions: in 71.8% in low-grade dysplasias adjacent to invasive carcinoma and in 94.4% in high-grade dysplasias adjacent to invasive carcinoma. Moreover, two of the four animals with low-grade dysplasia exclusively, and the four with high-grade dysplasia (one with carcinoma in situ) also had epithelial buds. In two specimens, invasive carcinoma was found to originate at the tip of the irregular buds with dysplasia. Similar histologic events have been found in chemically induced squamous esophageal carcinomas in rodents and in early squamous carcinoma in humans. It is therefore suggested that there is a close association between the degree of squamous cellular atypia, the formation of epithelial buds, and the progression toward invasive carcinoma in the esophagus.