The microcystic, elongated and fragmented (MELF) pattern of invasion: a single institution report of 464 consecutive FIGO grade 1 endometrial endometrioid adenocarcinomas

MELF invasion has been associated with non-vaginal recurrences and lymph node (LN) metastases in multi-institutional case control studies, but has not been well examined in large single institution cohorts. Hysterectomy specimens with FIGO 1 endometrioid endometrial carcinoma (EEC) and lymphadenectomies from 2007 to 2012 were identified. Electronic medical records and histologic slides were reviewed. Of 464 identified cases, 163 (35.1%) were noninvasive, 60 (12.9%) had MELF, 222 (47.8%) had a component of the infiltrative invasion pattern without MELF, 13 (2.8%) had pure pushing borders of invasion, 5 (1.1%) had pure adenomyosis-like invasion, and 1 (0.2%) had pure adenoma malignum-like invasion. Sixteen cases had LN metastases. Significantly more MELF cases had positive LNs than non-MELF cases overall (18.3% vs 1.2%, p