Characterization of High-grade Serous Carcinoma Involving the Ovarian Surface Epithelium-peritoneal Junction

Junctions between different types of epithelia are hotspots for carcinogenesis. The peritoneal mesothelium of the mesovarium transitions to the ovarian surface epithelium at the ovarian hilus (the ovarian surface epithelium-peritoneal junction). There are limited histologic data on this junction in humans. We examined 143 examples of this junctional region in 76 patients with normal ovaries and in 150 patients with extrauterine high-grade serous carcinoma (HGSC). In the absence of significant pathologic processes in the region, this is normally a clearly demarcated, quiescent junction that is usually present directly over the interface of the ovarian stroma with the fibrovascular tissue of the mesovarium. When the ovarian surface epithelium (OSE) and mesothelial linings are well-preserved, the epithelial change at this junction is clearly visible when the OSE is cuboidal or columnar (seen in 79%). When the OSE is flat, no junction is visible (21%). The junction is sharply demarcated in 69%, and in 10% the OSE displays a progressively shorter epithelial height in its transition to the flat mesothelium. Transitional cell metaplasia occurs in the immediate vicinity in 11% of cases. In women with HGSC, tumor was present within 2 mm of this region in 41%. Carcinoma was confined to the ovarian/peritoneal surface in 15% and invaded the stroma without surface involvement in 16%. Carcinoma involved both the surface and invaded the underlying stroma in 11%. In our previous report from this cohort, 40% had serous tubal intraepithelial carcinoma (STIC). In the junctional region, intraepithelial HGSC was seen at the ovarian or peritoneal surface or within ovarian surface epithelial inclusions in 7 cases. Among these 7, fallopian tube tissue was evaluable in 5, and STIC was present in 2 (40%). Our findings characterize the histologic features of the normal ovarian surface epithelium-peritoneal junction and the involvement of this region in extrauterine HGSC.