Studies of the incidence of spontaneous pancreatic tumours in ageing CD rats.

A survey of the incidence of spontaneous pancreatic tumours in CD rats was carried out. The survey revealed islet cell adenomas to be the most common of pancreatic tumours with a higher incidence in untreated males (11.7% in comparison to in females 5.5%). 9040 untreated and 24578 treated rats were included in this survey. These rats were from two year carcinogenicity studies over a 15 year period. The sex difference appeared also in the incidence of islet cell carcinoma (males 2.4% vs females 1%). The third type of tumour was exocrine adenoma with an incidence of 2% in males, 0.1% in females. The last type, which was very rare in this strain, was exocrine carcinoma (0.08% in males, 0.02% in females). The tumour incidences were more in rats killed at termination than in those died or killed earlier during the study suggesting a late onset of these tumours. Exocrine carcinoma was rarest of all pancreatic tumours. In contrast to man, rat pancreatic tumours were not life-threatening in rats, except for exocrine carcinoma. Pancreatic tumours are somewhat age-related as they were very rare in young rats and appeared mainly in rats over 70 weeks of age. Cystic exocrine adenoma, cystic or duct exocrine adenocarcinoma reported in man, were not seen in rats. Exocrine tumours are fatal tumours in man with very poor prognosis. Pancreatic carcinomas in rats mostly showed only local invasion. On very rare occasions they showed metastasis in to liver, lung and bone marrow. Ductal/cystic exocrine carcinoma of man showed metastasis to liver, peripancreatic lymph nodes, lymphatics, skeletal muscle and the lung. Exocrine adenocarcinoma in man was twice as common in males as in females, comparable to the general incidence of pancreatic tumours in rats. Islet cell tumours in man show no clear difference between males and females which is in contrast to rats. Both in man and in rats pancreatic tumours appear to occur in the latter half of life span.