Proliferating (LMP) mucinous tumors of the ovaries with microinvasion: morphologic assessment of 13 cases

From a consecutive series of 124 proliferating (low malignant potential) mucinous ovarian tumors, 13 FIGO stage Ia tumors exhibited 1 or more microfoci of stromal invasion. The proliferating mucinous tumors with microinvasion were of intestinal (7/88), endocervical-like (4/26), or mixed epithelial differentiation (2/10) and were more likely to show high-grade (10/42) than low-grade (3/82) epithelial proliferative changes. Morphologically, foci of microinvasion were characterized by single or small groups of epithelial cells in the tumor stroma. These cells were accompanied by a sparse lymphocytic infiltrate and stromal desmoplasia in their immediate vicinity and by a greater degree of nuclear anaplasia in the invading cells and in the lining cells of the nearby glands or cysts than was present elsewhere in the tumors. Focal inflammatory and degenerative changes, commonly seen in ovarian mucinous tumors, were discriminated from microinvasive carcinoma by the nature of the inflammatory response, the presence of stromal mucin deposits, and the absence of nuclear anaplasia. Follow-up was available in 10 of 13 cases (mean 7.5 years) and did not identify any adverse clinical consequences for the patients.