Lymphatic vascular invasion in ovarian serous tumors of low malignant potential with stromal microinvasion: a case...

Stromal microinvasion in ovarian serous tumors of low malignant potential (S-LMP) stratifies patients at long-term risk for disease progression independent of stage and primary ovarian histology. Despite the histologic impression and often-quoted incidence of lymphatic vascular invasion (LVI) in S-LMP with stromal microinvasion, there has been no formal evaluation in a case control series of S-LMP. The presence and extent of (LVI) was assessed in 20 S-LMP with stromal microinvasion and 20 S-LMP case controls without stromal microinvasion and compared with a series of low-grade and high-grade serous carcinomas using D2-40 monoclonal antibody recognizing podoplanin, a novel lymphatic endothelial marker. S-LMP case controls were matched for primary ovarian histology (usual vs. micropapillary), International Federation of Gynecology and Obstetrics (FIGO) stage, and age (best possible match). The patterns of stromal microinvasion included individual eosinophilic cells and cell clusters, cribriform, simple and noncomplex branching papillae, and inverted macropapillae. Immunohistologic staining with D2-40 monoclonal antibody clearly identified intratumoral LVI in 12/20 (60%) S-LMP with stromal microinvasion and 0/20 S-LMP without stromal microinvasion. Although only 4/13 (31%) low-grade serous carcinomas and 7/20 (35%) high-grade serous carcinomas had intratumoral LVI, hilar LVI was more common in the carcinomas (15% low-grade; 69% high-grade). Intratumoral LVI in S-LMP ranged from focal (6 cases) to multifocal (6 cases, maximum of 5 discrete foci) in any 1 section and included isolated single cells, simple papillae, and in 1 case, cribriform glands. Multifocal LVI was identified in 1 study patient who was pregnant. One of the 12 S-LMP patients with LVI had an intra-abdominal recurrence with high-grade disease at 16 months; whereas all other patients with follow-up were free of disease. LVI in ovarian S-LMP was significantly associated with the presence of stromal microinvasion (P<0.0001) and is independent of age, stage, primary ovarian histology, and pattern or extent of microinvasion. The presence of LVI in microinvasive S-LMP corroborates the view that microinvasion represents an early, but very low risk, invasive process that morphologically links S-LMP and low-grade serous carcinoma.