Interval cancers in a national colorectal cancer screening programme

Abstract

Background: Little is known about interval cancers (ICs) in colorectal cancer (CRC) screening. Objective: The purpose of this study was to identify IC characteristics and compare these with screen-detected cancers (SCs) and cancers in non-participants (NPCs) over the same time period. Design: This was an observational study done in the first round of the Scottish Bowel Screening Programme. All individuals (772,790), aged 50-74 years, invited to participate between 1 January 2007 and 31 May 2009 were studied by linking their screening records with confirmed CRC records in the Scottish Cancer Registry (SCR). Characteristics of SC, IC and NPC were determined. Results: There were 555 SCs, 502 ICs and 922 NPCs. SCs were at an earlier stage than ICs and NPCs (33.9% Dukes' A as against 18.7% in IC and 11.3% in NPC), screening preferentially detected cancers in males (64.7% as against 52.8% in IC and 59.7% in NPC): this was independent of a different cancer site distribution in males and females. SC in the colon were less advanced than IC, but not in the rectum. Conclusion: ICs account for 47.5% of the CRCs in the screened population, indicating approximately 50% screening test sensitivity: guaiac faecal occult blood testing (gFOBT) sensitivity is less for women than for men and gFOBT screening may not be effective for rectal cancer.

Screen‐detected and interval colorectal cancers in England: Associations with lifestyle and other factors in women in a large UK prospective cohort

“…8,9,[18][19][20] Our finding that smoking is related to risk of gFOBt interval, but not of screendetected, cancers is consistent with the emerging picture of molecular/morphological type-specific tumours which appear to behave differently both in terms of aetiology, and of screening. For FOB programmes, this may include tumours which either do not bleed sufficiently for detection, or whose location (more proximal, or rectal) or gross morphology mean that it is less likely either that faecal haemoglobin is present in a detectable form, or that the lesion is detected at diagnostic colonoscopy.…”

“…8 To study factors associated with screen detected cancer, we calculated adjusted risk ratios (henceforth referred to as relative risks, RRs) and 95% confidence intervals (CIs) using logistic regression. Unadjusted incidence rates for FOBt interval cancer, by age, were obtained using follow-up from the (gFOBt negative) BCSP screening episode start date for 2 years or until the first of date of death, emigration, next bowel cancer screening programme invitation, or date of diagnosis of any other cancer, if sooner.…”

“…Some features of screen-detected and interval colorectal cancers have been reported from England 6,7 and from the similar screening programme in Scotland, 5,8,9 but the screening programmes collect only limited information on individual participant characteristics which may be related to cancer detection. Using data from the NHS Bowel Cancer Screening Programme with electronic linkage to an on-going large UK prospective cohort, the Million Women Study, we report here tumour characteristics, including stage, grade, location and morphology, and relationship with lifestyle and other personal factors, for colorectal cancers detected at screening and in the interval between screens among 630,000 women screened in England between 2006 and 2012.…”

Overview of colorectal cancer screening

“…produces the same positivity rate in the population) it performs better than gFOBT in the detection of adenomas [4], thus enhancing the ability of the screening programme to prevent CRC.In terms of clinical impact, the screening programme has increased the proportion of CRCs diagnosed at an early stage. In a mature gFOBT programme, which consists of a combination of prevalence and incidence screening, around 35% of screen-detected cancers are diagnosed at Dukes A as opposed to 11% in the symptomatic population [5]. Indeed, in the region of 16% of screen-detected cancers are polyp cancers which are completely removed by colonoscopic polypectomy, usually at the same time as the colonoscopy organized in response to a positive gFOBT or FIT result.…”

“…In addition, of course, it results in a degree of overdiagnosis, i.e. some patients will be diagnosed with disease from which they were never destined to die.Screening programmes in the UK are not perfect; the sensitivities at which gFOBT and FIT operate in order to avoid overwhelming the colonoscopy services mean that there are a significant number of interval cancers [5]; in the vast majority of cases these are undoubtedly cancers that were missed by the most recent screening test. For this reason, there is worldwide interest in developing tests for CRC that are more sensitive and specific than those in current use.Of course, colonoscopy as a screening test is highly sensitive (few false negatives) and specific (false positives are extremely rare).…”