Proliferative heterogeneity of human renal cell carcinomas and prevalence of ras gene point mutations.

The variable prevalence and a possible stage-dependent increase of ras gene point mutations in human tumors might correspond to clonal growth advantages of ras-activated cells. Tumor areas with activated ras genes might thus differ in proliferative activity from those lacking ras gene activation. This hypothesis is studied in a series of human renal cell carcinomas that had been used previously for an analysis of proliferative compartments after post-operative vascular [3H]/[14C]thymidine perfusion [Rabes et al. (1979) Cancer 44: 799-813]. The growth fraction of different subcompartments of these tumors was studied by immunohistochemistry with mib1 antibody, recognizing a fixation- and embedding-resistant epitope of Ki-67 protein. Thirty subpopulations of 14 human renal cell carcinomas that exhibited a broad spectrum of proliferative activity were chosen for an analysis of the prevalence of K-ras point mutations in exon 1 by a mutation-enriching primer-mediated restriction-fragment-length-polymorphism analysis and/or direct sequencing of polymerase-chain-reaction-amplified material. The combined autoradiographic and immunohistochemical analysis confirmed the intra- and intertumoral proliferative heterogeneity. Compared to [3H]/[14C]thymidine labeling indices, mib1 labeling indices are higher. The ratio of mib1 to [3H]/[14C]thymidine labeling indices varies from 1.9 to 4.1 for the individual tumor subcompartments. However, neither in K-ras codons 12/13 nor in adjacent codons did we detect any mutations in the various tumor compartments. The results suggest that neither mode of proliferation nor type of differentiation is related to K-ras exon 1 point mutations in human renal cell carcinomas.