A different approach to tumour suppression. The Alexandra Kefalides Memorial Lecture.

When tumour cells are fused with normal ones, malignancy is suppressed. It has been shown that this suppression is associated with the imposition on the hybrid cell of the terminal differentiation programme of the normal parent cell. We report here the consequences of imposing the synthesis of keratin 1 and keratin 10, markers of terminal differentiation in the epidermal keratinocyte, on malignant cells of keratinocyte and non-keratinocyte lineage. We find that there is extreme selection in vivo against cells making keratin 1: tumours arising from inocula of such cells are invariably produced by the selective overgrowth of cells in which keratin 1 synthesis has been drastically reduced, usually to trace levels. No such selection operates against keratin 10. It is possible that if substantial synthesis of keratin 1 could be induced in malignant cells in a clinical context, some therapeutic benefit might accrue.