Some recent progress in the analysis of malignancy by cell fusion.

Malignancy, as measured by the ability of cells to grow progressively in vivo, is intimately linked to the presence of a structural abnormality in the polysaccharide moiety of one particular membrane glycoprotein. This abnormality is present in a wide range of different tumours; it co-segregates with malignancy in all crosses between malignant and non-malignant cells that have so far been tested; and it remains linked to malignancy in a stringent new test in which non-malignant variants are selected from tumour cell populations by the use of a lectin. Current work indicates that the abnormal membrane glycoprotein is, in all probability, one of the glucose transport proteins.