Frequency of spontaneous tumours in Wistar rats in 2-year studies.

Tumours occurring in 1270 male and 1270 female control rats of the strain Wistar (BOR:WISW (SPF Cpb), breeder: Winkelmann, Borchen), which had been employed in 22 different 2-year studies, were compiled on the basis of histopathology reports. 1261 male and 1259 female rats were evaluated. The remaining animals were unavailable due to autolysis. A total of 1485 tumours (722 in males, 763 in females) were seen in 1165 rats (570 males, 595 females), of which 333 were classified als malignant (119 in males, 214 in females). About 70% of all primary tumours were located in the pituitary, thyroid gland, adrenal glands and uterus. Average frequencies of primary tumours: pituitary 19.8% (18.0% in males, 21.5% in females), uterus (excluding polyps) 11.8%, thyroid gland 9.0% (9.3% in males, 8.7% in females), adrenal glands 8.1% (12.7% in males, 3.5% in females), testes 7.2%, ovaries 3.5%, mammary glands 3.1% (0.1% in males, 6.1% in females) and various other organs having tumour frequencies of less than 3%. Male rats exhibited strikingly more tumours of the adrenal glands, brain, skin, parathyroid glands, endocrine and exocrine pancreas, heart, spleen and lung, while tumours of the pituitary, vascular tissue and thymus were predominant in females. A comparison of these data with those from preceding 2-year studies in Wistar rats shows a certain increase in primary tumours of the mammary glands, parathyroid glands, exocrine pancreas, endocard, brain and vascular tissue.