Oncogene activation in malignant transformation: a study of H-ras in human breast cancer.

Two types of oncogene activation can occur in tumors. Quantitative changes have been demonstrated in a variety of animal and human tumors using molecular hybridization and immunohistochemical analyses. Qualitative changes in oncogene expression have also been found in a variety of tumors. In this study the existence of point mutations and other genetic changes in the H-ras1 gene in human breast tumors is demonstrated using oligonucleotide hybridization analysis. The role of quantitative and qualitative changes in oncogene expression in the multistep process of cancer is evaluated in view of these new findings.