SOMATIC MUTATIONS DETECTED BY MINISATELLITE AND MICROSATELLITE DNA MARKERS REVEAL CLONAL INTRATUMOR HETEROGENEITY IN GASTROINTESTINAL CANCERS

We investigated clonal intratumor heterogeneity by comparing different areas of each tumor in 20 gastrointestinal cancers from female patien ts (1 esophageal cancer, 5 stomach cancers, and 14 colorectal cancers) . In all 19 cases informative for X-inactivation analysis with the M27 beta and/or the phosphoglycerate kinase probes, the tumors were clona l. Separate areas from a given tumor showed identical X-inactivation p atterns, providing evidence for its single-cell origin. Of 20 cancers, 11 showed p53 gene mutations (base pair insertions, point mutations, and one case of a base pair deletion) in exons 5-8. A particular p53 g ene mutation was identical in all tumor areas investigated per case. T he minisatellite probes detected Loss of heterozygosity or new mutant alleles at 1p33, 1q21, 5q35, 17p13, or 18q21, In seven cases mutations at particular loci were restricted to one or two areas per tumor, whi le in another seven cases they were common to all tumor areas. Loss of heterozygosity or new alleles detected at the microsatellite loci D2S 123, D3S1611, D5S107, D17S261, or D18834 [(CA)(n) repeats] were common to all tumor areas in 7 of 19 cases. In another seven cases, however, microsatellite mutations at these loci were restricted to one to thre e areas per tumor. Tracing clonal intratumor heterogeneity would permi t one to study the hierarchy of mutational events in cancers where no premalignant lesions can be harvested. Most important, our study indic ates that clonal intratumor heterogeneity might lead to sampling error s in the molecular diagnosis of cancer biopsy specimens when using min i- or microsatellite markers.