[Occurrence of spontaneous tumours in the rat strain Chbb: THOM (SPF) (author's transl)].

400 albin rats (200 male, 200 female) of the strain Chbb: THOM (SPF) were investigated for the occurrence of spontaneous tumours over a period of almost three years. On day 750 of the study 78% of the male and 84% of the female animals were still alive. In 295 tumour hosts (73.8%) we discovered a total of 419 tumours. Several primary tumours were observed in 97 animals. The examinations revealed 240 tumours in the male and 179 tumours in the female rats. The highest tumour rate of 34.5% was established for adenomas of the interestial cells of Leydig in the testes. In female animals mammary tumours were the most frequent type of tumour, accounting for 31%. Talking into account the life expectation of the rats as well as the type and frequency of the tumours these results prove the suitability of this strain for carcinogenicity studies.