To investigate the clinicopathologic features of microcystic, elongated and fragmented (MELF) pattern invasion of endometrial adenocarcinoma.

HE and immunohistochemistry staining method were used to analysis morphologic features and immunophenotype of 72 patients of endometrial adenocarcinoma with MELF pattern invasion, and chi-square test was used to analysis the clinicopathologic features.

The mean age of 72 patients was 54 years (40 to 70 years). Thirty-two patients were pre-menopausal and 40 were post-menopausal. According to the FIGO staging system (2014), 32 cases(44.4%)were at stage Ⅰ, 22 cases(30.6%)at stage Ⅱ, 17 cases(23.6%)at stage Ⅲ and 1 case(1.4%) at stage Ⅳ. Microscopically, MELF invasion showed microcystic, elongated slit-like or fragmented glands in myometrium and their lining cells usually were cube or flat, as well as the single or clusters of eosinophilic tumor cells mimicking histocytes. In addition, a fibromyxoid or inflammatory stromal response was often present.Immunohistochemical staining showed that MELF invasion was positive for p16, CA125 and CA19-9, but negative for ER, PR and p53.Compared with non-MELF pattern invasion, significant differences were noted in menopause pausimenia, FIGO stages, deep invasion into myometrium, lymph metastasis, lymphovascular space invasion (LVSL), serum CA125 and CA19-9 in patients with MELF pattern invasion (all P<0.05).

MELF pattern invasion of endometrial adenocarcinoma is characterized by advanced FIGO stage, deep myoinvasion, high metastasis rate to lymph node and LVSL. Pathologists should recognize the MELF invasion and evaluate the depth of myometrium of infiltration and LVSL with special attention to the presence of MELF invasion with necessary immunohistochemistry for more accurate pathological diagnosis.

Endometrial neoplasms; Immunohistochemistry; Diagnosis, differential