Relation of squamous differentiation in endometrioid carcinoma with MELF pattern to a high ratio of lymph node metastasis

One of the known histological patterns of endometrioid carcinoma (EC) in uterine corpus cancer is MELF (microcystic, elongated, and fragmented). MELF is associated with lymphovascular invasion and lymph node metastasis. Besides MELF, it is also known that squamous differentiation (SD) often occurs in EC. SD is known to be no significant difference in the frequency of lymph node metastasis in EC. However, there have been no previous reports on the association between MELF and SD. In this research, we investigated the presence of SD in MELF using an antibody to CK5. We examined 28 cases of EC with MELF pattern, in which 15 cases showed SD. Moreover, the relation of lymph node metastasis to SD was examined. Lymph node dissection was performed in 27 out of 28 cases. Among them, 12 cases showed lymph node metastasis. The ratio of lymph node metastasis was significantly higher in EC with SD (64.3 %, 9 in 14 cases) than EC without SD (23.1 %, 3 in 13 cases). In this study, we first showed the association between SD and MELF and that MELF with SD is associated with a high ratio of lymph node metastasis. It is clinically relevant to recognize that MELF with SD is aggressive with a high ratio of lymph node metastasis.