Lewis rats of the inbred strain LEW/Han: life expectancy, spectrum and incidence of spontaneous neoplasms.

Although Lewis rats are frequently used in biomedical research, little is known about their life-data and spontaneous pathology. Therefore, it was the aim of this study to determine the life expectancy, spectrum and incidence of spontaneous neoplasms of the inbred rat strain LEW/Han. A total of 629 LEW/Han rats (305 females and 324 males) from a specified pathogen-free breeding colony were kept from weaning up to their natural death under defined environmental conditions. A complete histological examination was performed on all organs and macroscopically altered tissues of all animals which died during the first three years of the study. These were 296 female (98%) and 213 male (66%) rats. The mean lifespan of the females (27.7 +/- 5.1 months) was significantly shorter than that of the males (32.5 +/- 6.6 months). In both sexes, the lifespan was mainly determined by the occurrence of neoplasms. Of the large spectrum of 52 histologically different tumour types, the highest incidences were observed for adenomas of the pituitary gland and adenomas/adenocarcinomas of the adrenal cortex in both sexes, mammary gland tumours and endometrial carcinomas in females, and C-cell adenomas/adenocarcinomas of the thyroid gland and tumours of the haemopoietic system in males. Of these, the high incidences of tumours of the haemopoietic system in males (27.7%) and of endometrial carcinomas in females (45.2%) should be considered as characteristic features of the strain.