Chronochemotherapy of N-nitrosomethylurea-induced mammary tumors in rats. II. Circadian treatment with cyclophosphamide.

The chemotherapeutic effectiveness of intraperitoneal administration of cyclophosphamide (CY) (100 mg/kg) was evaluated, on a circadian basis, on the N-nitrosomethylurea (NMU)-induced mammary tumors in female Wistar rats. Untreated rats showed a progressive increase in the mean tumor number/rat, tumor area and total tumor area/rat. The average number of tumors/rat was significantly lower in the rats treated with CY at 02:00 h than the values obtained in the control group days 21 and 28, and than that observed at the end of the 4-week period of study in the rats treated with CY at 20:00 h. Average tumor area and total tumor area/rat in all groups of treated rats were lower than those in the untreated animals, though without significant differences amongst those treated with CY. The body weight remained constant throughout the 4-week period of study in the control group, while a transient reduction was registered after CY administration.