Mucinous adenocarcinoma: A unique clinicopathological subtype in colorectal cancer

Abstract

Mucinous adenocarcinoma (MAC) is a unique clinicopathological subtype of colorectal cancer, which is characterized by extracellular mucinous components that comprise at least 50% of the tumor tissue. The clinical characteristics, molecular features, response to chemo-/radiotherapy, and prognosis of MAC are different from that of non-MAC (NMAC). MAC is more common in the proximal colon, with larger volume, higher T-stage, a higher proportion of positive lymph nodes, poorer tumor differentiation, and a higher proportion of peritoneal implants compared to NMAC. Although biopsy is the main diagnostic method for MAC, magnetic resonance imaging is superior in accuracy, especially for rectal carcinoma. The aberrant expression of mucins, including MUC1, MUC2 and MUC5AC, is a notable feature of MAC, which may be related to tumor invasion, metastasis, inhibition of apoptosis, and chemo-/radiotherapy resistance. The genetic origin of MAC is mainly related to BRAF mutation, microsatellite instability, and the CpG island methylator phenotype pathway. In addition, the poor prognosis of rectal MAC has been confirmed by various studies, and that of colonic MAC is still controversial. In this review, we summarize the epidemiology, clinicopathological characteristics, molecular features, methods of diagnosis, and treatments of MAC in order to provide references for further fundamental and clinical research.

Keywords: Mucinous adenocarcinoma; Colorectal cancer; Mucin; Microsatellite instability; Magnetic resonance imaging; Treatment

Core tip: Colorectal mucinous adenocarcinoma (MAC) is a unique clinicopathological subtype in colorectal cancer. MAC exhibits a higher frequency of microsatellite instability, higher CpG island methylator phenotype of high degree, higher frequency of BRAF and KRAS gene mutations, and lower frequency of TP53 mutations. One of the most important features of MAC is the aberrant expression of a large number of mucins, including MUC1, MUC2 and MUC5AC. We discuss the epidemiology, clinicopathological characteristics, molecular features, methods of diagnosis, and treatments of MAC in order to provide references for further fundamental and clinical research.