Morphogenesis of Esophageal Carcinoma Induced by N‐Methyl‐N′‐nitro‐N‐nitrosoguanidine in the House Musk Shrew, Suncus murinus (Insectivora)

The histological changes occurring in the esophageal mucosa of shrews (Sitncun murinus) after N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG) treatment were investigated sequentially. Six‐week‐old female shrews were given a 50 %mUg/ml MNNG solution as drinking water for 30 weeks, and 5 selected at random were killed at 10 and 20 weeks of age, and thereafter at 5‐week intervals until 45 weeks of age. Controls were killed at 45 weeks of age. The MNNG‐induced esophageal lesion in shrews began from hasal cell hyperplasia at 20 weeks of age, followed by dysplasia occurring at 25 weeks of age, then progressed toward intraepithelial carcinoma to invasive squamous cell carcinoma at 35 weeks of age. Apparent sequential dysplasia‐carcinoma transition was seen. Papillomas were seen from 25 weeks of age but there was no evidence of papilloma‐carcinoma sequence. Five MNNG‐untreated shrews killed at the end of the experiment were free of esophageal tumors.