Mucinous carcinoma of the rectum: a distinct clinicopathological entity.

PURPOSE: The definition of mucinous tumours relies on quantification of the amount of mucus produced by neoplastic cells within the rectum. This has changed over the years to include varying degrees of mucin production. The inconsistency of diagnosis has led to conflicting reports in the literature regarding clinical outcomes and treatment response. A universally accepted definition and improved imaging and surgical techniques in the last decade are now challenging the traditional view of these tumours. The aim of this review was to present the current evidence on the clinicopathological characteristics of mucinous tumours of the rectum.
METHODS: A systematic review was conducted using Preferred Reporting for Systematic Reviews and Meta-Analyses guidelines. A literature search was performed using the Ovid SP to search both EMBASE and MEDLINE databases, Google Scholar and PubMed to find all studies relating to mucinous carcinoma of the rectum. The search dates were between 1 January 1965 and 1 March 2013.
RESULTS: Mucinous tumours comprise 5-20 % of all rectal cancers and commonly present at a more advanced stage and in younger patients. They are readily identified on MRI, and the diagnosis is confirmed on histological analysis, demonstrating more than 50 % of extracellular mucin within the tumour complex. They carry an overall worse prognosis compared to adenocarcinoma of the same stage. The response to oncological treatment remains controversial.
CONCLUSION: Mucinous tumours of the rectum are less well understood than non-mucinous adenocarcinoma. This is due to the inconsistent histopathological definitions of the past making comparison of clinical outcome data difficult. They remain challenging to treat and are associated with a poor prognosis. A universally accepted definition and the role of imaging techniques such as MRI to accurately detect mucinous tumours are likely to lead to a better understanding of these cancers.