Microinvasion in low malignant potential tumors of the ovary

The presence of microinvasion (Mi) has not previously been investigated in nonserous low malignant potential (LMP) tumors of the ovary. In serous LMP tumors (SLMP), Mi has not worsened the prognosis compared with usual SLMP in previous reports. In a retrospective clinicopathologic review of 126 cases of serous and mucinous LMP (MLMP) tumors of the ovary, the authors identified 14 cases with Mi: seven of 72 SLMP, four of 44 mucinous intestinal LMP (MILMP), and three of 10 mucinous mullerian LMP (MMLMP). Tumors with Mi resembled usual LMP histologically except for small foci (up to 0.2 cm) in the stroma consisting predominantly of single cells or small clusters of cells, sometimes in a cribriform pattern. In SLMP-Mi, the cells had eosinophilic cytoplasm, and the stromal reaction was minimal/absent. In MILMP-Mi and MMLMP-Mi, nuclear staining was paler; the stroma often showed a fibrous reaction oredema, especially in MILMP-Mi. All 14 patients had follow-up (2.2 to 18.6 years) and were without evidence of disease. Careful screening of both mucinous and serous ovarian LMP can show Mi. Mi foci should be distinguished from true stromal invasion, pseudoinvasion, endothelial cells, decidual cells and histiocytes, and pseudomyxoma in mucinous LMP. Mi does not seem to worsen prognosis in MLMP and SLMP tumors of the ovary.