Two lines of Lewis lung carcinoma with a different potential to metastasize spontaneously to the lungs have been examined for their cytological and histological characteristics. Metastatic potential appears to be related with parenchymal organization of the primary tumours, since large haemorrhagic areas containing detached tumour cells and the absence of endothelialized capillaries are observed only in the line with high metastatic potential. At the same time, the cytological characteristics of the cells of the two tumour lines are similar, and do not seem to be related with metastatic potential. After treatment with the selective antimetastatic drugs ICRF-159 and DM-COOK, and with DTIC, the histological appearance of the line with high metastatic potential becomes similar to that of the line with low metastatic potential. These data seem to indicate that the early phases of tumour spread occurring in the primary tumour are of relevance for metastatic potential and control by antimetastatic drugs, and suggest that for DTIC such antimetastatic action may participate to its clinical antitumour effects.
