Editor's Choice

Abstract

A comparison of tumour and host prognostic factors in screen-detected vs non screen-detected colorectal cancer: a contemporaneous study. Mansouri D, McMillan DC, McIlveen E, Crighton EM, Morrison DS, Horgan PG.1 Current guidelines generally recommend screening for colorectal cancer from the age of 50, as there is compelling evidence that the benefits outweigh the risks. Screening can either prevent cancer by early polyp removal or improve disease-specific survival due to detection of early tumours. As prognosis in colorectal cancer is directly related to stage, the beneficiary effect of screening is by no means a surprise. I have been wondering for a long time, however, whether improved survival is also related to a different biological entity of screen-detected (SD) tumours, with better prognosis than non-screen-detected (NSD) cancer. After all, it might be possible that we are (also) looking at the effect of length-time bias (i.e. artificially improved cancer outcome due to the identification of indolent slow growing tumours). The study in this issue by Mansouri et al. assesses for the first time both host-factors and tumour-phenotype, in addition to tumour stage and site, within the context of a colorectal cancer screening programme. Compared to NSD tumours (both non-responders to screening and patients with interval tumours), patients with SD tumours had less advanced T-stage and less evidence of venous invasion. They had also less evidence of an elevated preoperative systemic inflammatory response. When adjustment was made for stage, however, the two key features representing phenotypically more aggressive tumours (i.e. venous invasion and poor differentiation) did not achieve statistical significance. Subgroup analysis comparing SD tumours with (more aggressive) interval tumours also did not show difference in prognostic factors when adjusted for stage. The conclusion was therefore drawn that the inherent biological characteristics of SD tumours do not differ from those of NSD disease. I agree, although it should be realized that the present study represents a population setting where compliance to the screening programme was just over 50%, and only a minority of interval tumours was detected, which might have influenced the results. So, although slightly reassured, I am still hoping for more studies which address this fascinating subject.