Benign ovarian serous tumors: a re-evaluation and proposed reclassification of serous "cystadenomas" and "cystadenofibromas"

OBJECTIVE: Serous cystadenomas and cystadenofibromas of the ovaries are currently regarded as neoplasms and are considered the most common ovarian neoplasms. The purpose of this study is to determine what proportion of benign serous tumors contain an epithelial proliferation (the hallmark of a neoplastic process in nearly all other sites) that can be considered neoplastic as opposed to reactive in nature. METHODS: An unselected series of 113 ovarian serous tumors (76 serous cystadenomas and 37 serous cystadenofibromas) were histologically evaluated. A 1-mm in diameter area of epithelial proliferation was considered potentially neoplastic. RESULTS: Eight tumors (7%) displayed at least 1 mm of epithelial proliferation (1% of serous cystadenomas and 19% of serous cystadenofibromas). CONCLUSION: The vast majority of benign serous tumors may not be bona fide epithelial neoplasms, but rather, may represent cystically dilated glandular inclusions (cystadenomas) and fibromas with epithelial inclusions (cystadenofibromas). A recently published study evaluating clonality in serous cystadenomas found that the vast majority are polyclonal and thus supports this hypothesis. These findings have important implications for the pathogenesis of ovarian cancer, for the distribution of ovarian neoplasms, and for the interpretation of molecular biological studies of ovarian tumors.