Two adjacent mutations at position 12 activate the K-ras2 oncogene of a human mammary tumor cell line

Among 10 human mammary tumor cell lines analyzed for transforming genes by transfection of NIH 3T3 cells, one carcinoma cell line, H-466B, established from an ascitic effusion of a woman with an adenocarcinoma of the breast was scored as positive. The transforming gene was identified as the K-ras2 oncogene. Nucleotide sequencing of exons 1 and 2 of the activated gene revealed two adjacent G----T transversions at the first and second position in codon 12 leading to the replacement of the normally encoded glycine by a phenylalanine. Since the phenylalanine substitution had never been observed in any type of tumor, this raises the question about the frequency as well as the cell type specificity of this K-ras2 activation in mammary tumors.