Interphase cytogenetic analysis of serous ovarian tumors of low malignant potential: comparison with serous cystadenomas and invasive serous carcinomas.

The cytogenetic and molecular genetic changes in serous tumors of low malignant potential (LMP) of the ovary have not been well characterized so far. Therefore, we analyzed 20 serous tumors of LMP, 10 invasive serous ovarian carcinomas, and 7 benign serous cystadenomas by nonisotopic in situ hybridization (seven different centromere-specific probes) as well as by flow and image DNA cytometry and compared the data with results of p53 and Ki67 immunohistochemistry, MYC DNA PCR analysis and with the clinical follow-up. All but two tumors of LMP were DNA cytometrically diploid; 9 of 10 invasive carcinomas proved to be DNA nondiploid (p < 0.0001). Nonisotopic in situ hybridization revealed a mean number of 1.5 chromosomal aberrations in tumors of LMP, which differed statistically significantly from cystadenomas (mean, 0.4) and from invasive carcinomas (mean, 3.4) (rho < 0.01). The main changes in tumors of LMP were +6 (7 of 18 cases) and +7 (6 of 19) followed by -3 (5 of 20), -1 (4 of 17) and +X (3 of 20). In the group of invasive carcinomas, the number of cases with signal gains for chromosomes 6 (5 of 8), 7 (7 of 10) and X (4 of 10) and signal loss for chromosome 1 (4 of 9) was even larger. In addition, statistically significantly more cases showed gain of 8 (5 of 10) and loss of 17 (5 of 10) (p < 0.05). Proliferative activity (Ki67 index) was positively correlated with the number of chromosomal aberrations (p < 0.05). There was no association between changes in the centromere signal number of chromosomes 8 and 17 and MYC DNA amplification and immunohistochemical p53 accumulation, respectively. Clinical follow-up showed prognostic differences between tumors of LMP and invasive carcinomas as expected (rho < 0.001) but did not reveal differences within the group of tumors of LMP with regard to the number or type of the chromosomal abnormalities detected. In conclusion, the patterns of chromosomal gains and losses in serous tumors of LMP and invasive serous carcinomas of the ovary do not seem random and suggest a close relation between these neoplasms compatible with sequential stages in a multistep model of ovarian carcinogenesis.