MELF Pattern of Myoinvasion in Endometrioid Endometrial Adenocarcinoma Is Associated with Low-Grade Tumors, Deep Myometrial Invasion and a Low Proliferative Index
Janet I Malowany, Amir Parsoei, Marcus Q Bernardini, Anthony Fyles, Marjan Rouzbahman. Toronto General Hospital, Toronto, Canada; University of Toronto, Toronto, Canada
Background: Low-grade and early-stage endometrioid endometrial adenocarcinoma (EEC) usually has a favorable outcome. There is a subset of patients with a microcystic, elongated and fragmented (MELF)-pattern of invasion that has been implicated with increased lymphovascular invasion (LVI) and lymph node metastases. Changes in immunohistochemical markers within MELF areas suggest these areas are distinct from the original tumor. This study characterizes the frequency of MELF-type invasion, its relationship with depth of myometrial invasion, LVI, changes in estrogen receptor (ER) status, E-cadherin and Ki67 expression.
Design: 286 cases of pure EEC were retrieved between 2001- 2011. The histological slides and clinical records were reviewed to record FIGO grade, depth of invasion, pattern of myometrial invasion, LVI and clinical outcome. A representative slide was selected to determine the expression of ER, E-cadherin and Ki67 within the tumor and in the MELF areas. Fisher's exact tests and student t-tests were used for statistical analyses.
Results: MELF was identified in 47 of 286 (16%) cases including 11 with focal areas of MELF. Tumors with MELF pattern were more likely to be grade 1 (76% v 51%), contain LVI and show invasion into outer half of myometrium. In FIGO grade 1 tumors, the MELF group was still more likely to contain LVI (62% v 26%, p<0.001) and invade into outer half of myometrium (65% v 33%, p<0.001). Disease recurrence and mortality were not significantly higher in MELF group. There was no significant difference in expression of ER and E-cadherin in MELF areas with the rest of the tumor. The proliferative index Ki67 appeared to be lower in at least 50% of cases in the MELF areas.
|LVI present||Outer half myometrial invasion|
|Total EEC (all grades)||29%||38%|
|MELF cases (all grades)||72%||74%|
|Grade 1 EECs||26%||33%|
|Grade 1 with MELF||62%||65%|