Microsatellite analysis in serous tumors of the ovary

Thirty-four serous ovarian neoplasms were analyzed for microsatellite instability (MIN) and loss of heterozygosity (LOH) at 20 chromosomal loci of eight different chromosomes, including the map positions of the six known mismatch repair genes. Twelve of the 20 (60%) serous ovarian tumors of low malignant potential (LMP) and 13 of 15 (87%) samples of serous ovarian carcinomas, taken from 14 patients, showed LOH at one or more of the analyzed microsatellite loci. In serous carcinomas, LOH of the dinucleotide repeat D7S521 was most frequent. Six of 20 (30%) LMP tumors were also affected by MIN at more than one locus, whereas in the carcinomas MIN was found only sporadically (p < 0.025). No correlation between increased occurrence of MIN and LOH at the chromosomal loci of the known mismatch repair genes were discovered for these LMP tumors. Although our observation regarding LOH frequency in serous LMP tumors and serous carcinomas is compatible with the hypothesis that serous LMP tumors might represent precursor lesions of invasive carcinomas, the results concerning the occurrence of MIN suggest that the mechanisms of tumorigenesis of some tumors of LMP are distinct from those in invasive serous carcinomas.