ROSENBERG (1977) put forward a hypothesis concerning the mechanism of anticancer activity of cis-platinum complexes in vivo. According to this hypothesis, the simple cytotoxic effect is accompanied by an enhanced expression of cancer antigens on the surface of malignant cells. Therefore, the observed regression of malignant growth is at least partly due to the immunological response of the organism. An example supporting this assumption is the growth kinetics of ascites sarcoma 180 in ICR mice after injection of cis-dichlorodiammine cis-platinum (Rosenberg, 1978). For 4 days following injection the number of tumour cells increases. From the 5th day it falls, reaching zero in a cured animal. According to Rosenberg, this result is consistent with the suggestion that surviving cells are destroyed by the immune system. The hypothesis implies the existence of a ready defensive mechanism which can be stimulated by cisplatin-induced changes in the malignant cell surface. In an attempt to test this hypothesis, we used cis-dichloro bis-(cyclopentylamine) platinum (II) (cis-PAD) and L5178Y-R murine leukaemic cells. These cells are very sensitive to cis-PAD in vitro (Szumiel, 1979) and form ascites tumours in DBA/2 mice. The Pt complex is effective in vivo in mice against leukaemi
