Invasive micropapillary component and its clinico-histopathological significance in patients with colorectal cancer.

Micropapillary components are located in distinct, empty spaces resembling lymphatic vessels and consist of clusters of cancer cells that adhere tightly to one another. These structures do not have a fibrovascular core. Invasive micropapillary components (IMPCs) exhibit reverse polarity, which results in a characteristic 'inside-out' structure. The aim of the present study was to examine the histological significance of the micropapillary component in colorectal carcinoma compared with conventional colorectal adenocarcinoma. Among 115 patients, 5 (4.3%) were diagnosed with a micropapillary colorectal component based on hematoxylin and eosin staining and immunohistochemical analysis. To exclude identification of poorly-differentiated clusters of adenocarcinoma cells in the lymphatic vessels, immunohistochemical analysis with D2-40 was performed, and epithelial membrane antigen was used to confirm the specific 'inside-out' structure of IMPCs. IMPCs were observed to positively correlate with histopathological type (P=0.001) and tumor invasion in venous vessels (P=0.033). Furthermore, the presence and number of lymph node metastases was greater in IMPC cases compared with conventional carcinoma cases; however, these differences were not statistically significant (P=0.087 and P=0.094, respectively). In addition, IMPC cases were not significantly associated with the presence of inflammatory infiltrate in the invasive front of the tumor (P=0.098). Therefore, the present study indicates that the IMPC serves a histopathological and prognostic role in the diagnosis of colorectal cancer due to its aggressive and invasive behavior. IMPC is rare in cases of colorectal cancer and remains a great diagnostic challenge in pathomorphology with further detailed investigation required in the future.