Tetrasomy 12 in ovarian tumors of thecoma‐fibroma group: A fluorescence in situ hybridization analysis using paraffin sections

Recent cytogenetical studies have indicated that trisomy 12 is a feature of ovarian tumors in the thecoma-fibroma group. Ten cases of these ovarian tumors were studied in total, including two thecomas, two fibrothecomas, four fibromas, one cellular fibroma and one fibrosarcoma, to clarify the relationship between polysomy 12 and proliferative activity in these tumors. Each formalin-fixed, paraffin-embedded tumor tissue was examined by fluorescence in situ hybridization to determine copy numbers of chromosome 12 and by immunohistochemical staining of Ki-67 for evaluation of tumor cell proliferation. Gains of trisomy 12 were found in seven of the 10 cases, and the percentage of cells with tetrasomy 12, but not that of cells with trisomy 12, was significantly and positively correlated with percentage of Ki-67-positive cells, but significantly and inversely correlated with patient age. These findings suggest that tetrasomy 12 is an age-related aberration of chromosome 12 in ovarian tumors of the thecoma-fibroma group, and that such tumors exhibit more active proliferation in younger patients.