The effect of cyclophosphamide on the growth and cellular kinetics of a transplantable rat fibrosarcoma.

The gross response of a transplantable fibrosarcoma (RIB(5)) in rats treated with a single dose of 10, 50, 100 or 200 mg/kg body weight of cyclophosphamide (CP) is reported. The variation in mitotic and tritiated thymidine ((3)H-TdR) labelling indices after a single dose of 100 mg/kg CP was studied. Examination of chromosome spreads has shown the time course of the visible damage to DNA caused by CP and a transient arrest of cells in G(2) was demonstrated by microdensitometry. The effects of 100 mg/kg body weight CP given in 2 equal doses separated by various time intervals were examined in an attempt to relate tumour response to its altered cellular state at the time of the second dose.