Advanced ovarian carcinoma: molecular evidence of unifocal origin

The clonal origin has sometimes been disputed in advanced epithelial cancers when multiple sites of peritoneal tumors were present because of the developmental similarity of the surface epithelium of the ovary and the peritoneal mesothelium. We have taken two independent approaches to study the clonality of advanced epithelial carcinoma. Tumor samples of both ovaries, and/or omentum, and/or peritoneum from nine patients were examined. The analysis of loss of heterozygosity (LOH) at 86 polymorphic chromosomal loci distributed on every chromosome revealed the loss of the same allele in every tumor of each patient when LOH was detected. In addition, we used a restriction-fragment-length polymorphism in an X-linked sequence (DXS255) to examine the pattern of X-chromosome inactivation based on the differential methylation of DXS255 in active and inactive X chromosomes. Inactivation of the same X chromosome in various tumors from the same patient was observed in each of the five informative patients. Our results strongly suggest that the advanced epithelial cancers are monoclonal in origin.