apoptosis and catastrophic cell death in benzoapyrenetransformed human breast epithelial cells apoptosis and mitotic death bi and multinucleation giant cells and micronucleation were investigated in human breast epithelial cell lines transformed by benzoapyrene bp bp1 bp1e and bp1e1 cells and in bp1 cells transfected with the charas oncogene bp1tras cells since bp induces apoptosis and the abnormal expression of ras genes elicits catastrophic mitosis both cell death phenomena were expected to occur in this system especially in bp1tras cells regardless of the cell line considered singlenucleate cells were found to be eliminated preferentially through apoptosis while bi and multinucleate cells were eliminated through catastrophic mitosis apoptosis and catastrophic mitosis were observed in all cell lines but were significantly more frequent in bp1tras cells the abnormal expression of haras in the latter cells may enhance in this system the effects of the bp apoptosis path reported for bptransformed hepa 1c1c7 hepatoma cells transfection with the ras oncogene also enhanced the mitotic disturbances which produced multi and micronucleation and mitotic death possibly because of the genomic instability promoted by this oncogene in the bptransformed cell line