Precursors in the ovarian stroma: another pathway to explain the origin of ovarian serous neoplasms.

Ovarian serous neoplasms are thought to arise from the fallopian tube or from the ovarian surface epithelium. The possibility of a third pathway-involving the mesenchymal-epithelial transition and mimicking the formation of the Müllerian duct-arose from observations gathered from our routine cases. The purpose of this study is to determine the association of precursors in the ovarian stroma with different types of ovarian serous neoplasms. Three hundred neoplasms, benign (25), borderline (63), and malignant ovarian serous neoplasms (40 low-grade serous carcinomas [LGSCas] and 172 high-grade serous carcinomas [HGSCas]), were reviewed. Clinicopathologic features analyzed included patient's age, tumor size, stage, histologic pattern, and possible precursors in the ovarian parenchyma (endosalpingiosis, inverted macropapillae, polyploid giant cancer cells, and simple cysts). All benign and borderline cases showed continuity with benign serous cysts or endosalpingiosis. In LGSCas, continuity with serous cysts was found in 29 (72%) of 40 cases, and inverted macropapillae were found in 12 (30%) of 40 cases. In untreated HGSCas, there was continuity with simple cysts in 42% of cases. In addition, these HGSCas contained polyploid giant cancer cells in 20% of cases. There were no different features in the ovaries in cases with or without serous tubal intraepithelial carcinoma. Our study shows that in a subset of cases, ovarian serous neoplasms and the Müllerian duct develop in similar fashion, originating from epithelial cells derived from the mesothelium, or occur de novo from structures derived from mesenchymal-epithelial transition.