Prevalence of ras gene mutations in human colorectal cancers

The Department of Medical Biochemistry and t Department of Organic Chemistry, State University of Leiden, Sylvius Laboratories, The Netherlands * The Oncology Center and t Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA A combination of DNA hybridization analyses and tissue sectioning techniques demonstrate that ras gene mutations occur in over a third of human colorectal cancers, that most of the mutations are at codon 12 of the c-Ki-ras gene and that the mutations usually precede the development of malignancy.