Endocervical Adenocarcinoma Showing Microcystic, Elongated, and Fragmented (MELF) Pattern of Stromal Invasion: A Single-Institutional Analysis of 10 Cases with Comprehensive Clinicopathological Analyses and Ki-67 Immunostaining

Abstract

Microcystic, elongated, and fragmented (MELF) pattern of invasion has seldom been documented in endocervical adenocarcinoma (EAC). The aim of this study was to analyze the clinicopathological characteristics of EAC showing MELF pattern. We collected the clinicopathological information of 10 cases of EAC with the MELF pattern and conducted polymer-based immunostaining for Ki-67 (dilution 1:200, clone MIB-1) on these cases. Ki-67 expression was assessed using the average estimation within the hotspot method. All tumors were human papillomavirus-associated EAC with Silva pattern C. All except one tumor exceeded 3 cm in size. Five tumors involved the entire thickness of the cervical stroma, and four tumors extended into the parametrium. Lymphovascular space invasion was identified in six cases. Two patients developed metastatic recurrences in the para-aortic lymph nodes and lungs, respectively. The MELF area showed significantly lower Ki-67 labelling index than that of a conventional tumor area. We confirmed our previous observation that the MELF area displayed lower proliferative activity than the conventional tumor area of EAC. We also demonstrated that patients with EAC showing MELF pattern had several adverse clinicopathological characteristics reflecting aggressive behavior. On the other hand, since the frequencies of post-operative recurrence and disease-related mortality that occurred during the follow-up period were relatively low, further investigations are warranted to clarify the prognostic value of MELF pattern in EAC patients.

Keywords: immunohistochemistry; mesonephric-like adenocarcinoma; mismatch repair; programmed cell death-ligand 1; targeted sequencing; uterus.

Figure 1

Flowchart of patient selection process. Among 97 patients with primary EAC, 8 were excluded from this study due to either mixed histology (three with small cell neuroendocrine carcinoma [SCNEC], two with adenosquamous carcinoma [ASC], and one with carcinosarcoma [CS]) or pre-operative treatment (two patients). We included 89 patients who underwent surgery for EAC in our institution. Slide review reveals that 10 cases of EAC displayed MELF pattern.

Figure 2

Histological types of EAC. (A) Usual type. (B,C) Usual type with MELF pattern. (D) Mucinous intestinal type. (E) Signet-ring cell type. (F) Invasive stratified mucin-producing type. (G) Gastric type. (H) Clear cell type. (I) Mesonephric type.

Figure 3

Histological features of MELF pattern in EAC. (A,B) Compared with the conventional tumor area showing well-developed, complex glandular architecture (upper one-third), the MELF area (orange arrows) displays a strikingly different structure. Note a poorly circumscribed, lobulated tumor border along the invasive front, with neoplastic glands not apparent at low-power magnification. (C) In the MELF area, the neoplastic glands seem to be variably collapsed or absent, and the stroma exhibits intense inflammatory reactions. (D) The lining epithelium of distorted or ruptured glands show a squamoid or histiocytoid appearance. A fibromyxoid response in the periglandular stroma is associated with mixed inflammatory infiltrates. (E) Some tumor cells scattered singly or forming small clusters resemble histiocytes. (F) Usual-type EAC characteristically shows human papillomavirus-infection-related histology, including apical mitotic figures (yellow arrows) and basal apoptotic bodies (blue arrows). Most of the tumor cells exhibit nuclear hyperchromasia and pleomorphism (inset). (G) Compared with a conventional tumor area, the tumor cells in the MELF area are round or polygonal with more abundant cytoplasm, resulting in a lower nuclear-to-cytoplasmic ratio. They exhibit smaller nuclei with mild pleomorphism, larger amount of eosinophilic cytoplasm, and intracytoplasmic vacuoles (green arrows). (H) Immunostaining reveals block p16 positivity in both the MELF (white arrows) and conventional invasion (black arrows) areas. Staining method: (A–G), hematoxylin and eosin staining; (H), immunohistochemical staining. Original magnification: (A,B), 20×; (C), 40×; (D), 100×; (E–G), 400×; (H), 100×.

Figure 4

Ki-67 immunostaining results of EAC with MELF pattern. (A,B) The MELF area (blue arrows) shows reduced proliferative activity compared to the conventional invasion area. Ki-67-positive tumor cells in the MELF area obviously number fewer than in the conventional tumor area. (C,D) The lining epithelium of the MELF glands (green arrows) rarely reacted with Ki-67, whereas the conventional neoplastic glands (left upper corner) intensely and uniformly express Ki-67. Staining method: (A,C) hematoxylin and eosin staining; (B,D) immunohistochemical staining. Original magnification: (A,B) 40×; (C,D) 100×.