Invasive micropapillary carcinoma of the extrahepatic bile duct and its malignant potential

Cholangiocarcinoma

Liver cancer represents the third leading cause of cancer-related death worldwide. Cholangiocarcinoma (CCA) is the second most common type of liver cancer after hepatocellular carcinoma, accounting for 10-15% of all primary liver malignancies. Both the incidence and mortality of CCA have been steadily increasing during the last decade. Moreover, most CCAs are diagnosed at an advanced stage, when therapeutic options are very limited.

CCA may arise from any tract of the biliary system and it is classified into intrahepatic, perihilar, and distal CCA, according to the anatomical site of origin. This topographical classification also reflects distinct genetic and histological features, risk factors, and clinical outcomes. This review focuses on histopathology of CCA, its differential diagnoses, and its diagnostic pitfalls.

Consensus and conflict in invasive micropapillary carcinoma: a case report and review of the literature

Invasive micropapillary carcinoma (IMPC) is an aggressive histologic subtype of adenocarcinoma that has been gaining increased attention over the past twenty years. It is important to recognize IMPC due to its strong association with early lymphovascular invasion (LVI), high risk of lymph node metastasis, perineural invasion and poor prognosis. Controversies regarding IMPC include differentiating from retraction artifact and mimics, clinical significance of proportion of micropapillary component (MC), pathogenesis, biologic nature of the entity and consequently terminology, etc. We herein present a case of rectal IMPC arising from a tubulovillous adenoma. Since HER2 over-expression has been reported in IMPC of the breast and the bladder but never in the colorectum, given the availability of HER2 targeted therapy, HER2 protein expression in our case is examined by immunohistochemical study which shows weak incomplete membrane staining in less than 5% of cells. Literature is reviewed with emphasis on colorectal IMPC as well as aforementioned controversial topics. In summary, more study is needed to resolve the conflicts and build consensus on IMPC.