Stromal nephromas and renal cell tumors in suckling and weaned rats.

Renal neoplasms with induction times ranging from 218 to 505 days appeared in 51 or 64% of 80 male Wistar rats in 3 groups which, when 1 or 7 days old, were given single s.c. injections of dimethylnitrosamine in dosages of 125 ;ug/animal or 10 mg/kg. In 44 male rats so treated after weaning at 21 or 70 days of age, tumor yields were scant and induction times exceeded 480 days, but dimethylnitrosamine dosage levels of 20 or 30 mg/kg produced renal tumors with induction times ranging from 286 to 550 days in 33 or 53% of 62 males in 4 groups also treated at 21 or 70 days of age. The hepatoma yield was small. Abdominal palpation was highly accurate for relatively early diagnosis of renal neoplasms. Ninety-two % of renal neoplasms in rats treated when sucklings were stromal nephromas; 41% of renal tumors in rats treated after weaning were of renal cell type. One stromal nephroma produced epithelial-containing pulmonary métastases.