Interval cancers in a population-based screening program for colorectal cancer in catalonia, Spain

Interval Cancer in Population-Based Colorectal Screening Programmes: Incidence and Characteristics of Tumours

The objective of this study is to evaluate interval cancer (IC) in colorectal cancer (CRC) screening, which is CRC diagnosed in an individual after having received a negative faecal occult blood test and before the next invitation to participate in screening. A follow-up study was conducted on a cohort of participants in the first three screening rounds of four colorectal cancer screening programmes in Spain, n = 664,993. A total of 321 ICs and 2120 screen-detected cancers (SCs) were found. The IC and SC rates were calculated for each guaiac (gFOBT) or immunochemical (FIT) test. A Cox regression model was used to estimate the hazard ratios (HR) of IC risk factors. A nested case-control study was carried out to compare IC and SC tumour characteristics. The IC rate was 1.16‱ with the gFOBT and 0.35‱ with the FIT. Men and people aged 60-69 showed an increased probability of IC (HR = 1.81 and HR = 1.95, respectively). There was a decreased probability of IC in individuals who regularly participated in screening, HR = 0.62 (0.47-0.82). IC risk gradually rose as the amount of Hb detected in the FIT increased. IC tumours were in more advanced stages and of a larger size than SC tumours, and they were mostly located in the cecum. These results may play a key role in future strategies for screening programmes, reducing IC incidence.

Optimizing the Design of a Repeated Fecal Immunochemical Test Bowel Cancer Screening Programme With a Limited Endoscopy Capacity From a Health Economic Perspective

OBJECTIVES

In 2016, it was announced that the fecal immunochemical test (FIT) would replace the guaiac fecal occult blood test in the UK Bowel Cancer Screening Programme. England has limited endoscopy capacity. This study informed decision making by determining the most cost-effective FIT screening strategy (age range, frequency, and FIT threshold) under a constrained endoscopy capacity.

METHODS

An economic model with a colorectal cancer natural history component was used to model 60 221 screening strategies with first screening at age 50 to 60 years, screening interval of 1 to 6 years, 3+ screening episodes, and FIT integer threshold of 20 to 180 μg hemoglobin/g feces. Screening strategies requiring the same endoscopy capacity were compared to determine the characteristics of the most cost-effective strategies.

RESULTS

With 50 000 annual screening referral colonoscopies, the 20 most cost-effective strategies had a starting age of 50 to 53 years, 2-yearly screening, 7 or 8 rounds of screening, and FIT threshold of 127 to 166. Compared with a 2-yearly screening interval, screening less frequently (3-, 4-, 5-, or 6-yearly) with a more sensitive FIT was less cost-effective.

CONCLUSIONS

The UK Bowel Cancer Screening Programme should use a 2-yearly FIT screening interval. When endoscopy capacity increases, the screening starting age should be reduced first followed by reducing the FIT threshold. These findings are relevant for other colorectal cancer screening programs with constrained endoscopy capacity.

Optimizing the colorectal cancer screening programme using faecal immunochemical test (FIT) in Flanders, Belgium from the “interval cancer” perspective

Background

Interval cancer (IC) is a critical issue in colorectal cancer (CRC) screening. We identified factors associated with ICs after faecal immunochemical test (FIT) screening and explored the impact of lowering FIT cut-off or shortening screening interval on FIT-ICs in Flanders.

Methods

FIT participants diagnosed with a CRC during 2013–2018 were included. Factors associated with FIT-ICs were identified using logistic regression. Distributions of FIT results among FIT-ICs were examined.

Results

In total, 10,122 screen-detected CRCs and 1534 FIT-ICs were included (FIT-IC proportion of 13%). FIT-ICs occurred more frequently in women (OR 1.58 [95% CI 1.41–1.76]) and ages 70–74 (OR 1.35 [1.14–1.59]). FIT-ICs were more often right-sided (OR 3.53 [2.98–4.20]), advanced stage (stage IV: OR 7.15 [5.76–8.88]), and high grade (poorly/undifferentiated: OR 2.57 [2.08–3.18]). The majority (83–92%) of FIT-ICs would still be missed if FIT cut-off was lowered from 15 to 10 µg Hb/g or screening interval was shortened from 2 to 1 year.

Conclusions

FIT-ICs were more common in women, older age, right-sided location, advanced stage and high grade. In Flanders, lowering FIT cut-off (to 10 µg Hb/g) or shortening screening interval (to 1 year) would have a minimal impact on FIT-ICs.

Interval colorectal cancers after negative faecal immunochemical test in a 13-year screening programme

OBJECTIVE

To assess faecal immunochemical test sensitivity for cancer in a very large population-based cohort followed up for six rounds with biennial faecal immunochemical test repetition.

METHODS

This study is based on interval colorectal cancers diagnosed in a cohort of subjects aged 50-69 undergoing repeated faecal immunochemical test screening (six rounds) from 2002 to 2015. Test sensitivity was calculated using both the Proportional Interval Cancer Rate and the Interval Cancer Proportion method.

RESULTS

Among 441,647 faecal immunochemical tests (123,347 individuals), 150 interval colorectal cancers were detected after a negative faecal immunochemical test. Interval colorectal cancer incidence rate was 1.87 per 10,000 person-years (95%CI: 1.60-2.20), and it was higher during the second interval year (rate ratio: 1.78; 95%CI: 1.28-2.47), for proximal locations (rate ratio: 3.00; 95%CI: 1.92-4.68), and among 60-71 year old subjects (rate ratio: 2.37; 95%CI: 1.61-3.50). The Proportional Interval Cancer Rate was 13.1%, with an overall faecal immunochemical test sensitivity of 86.9% (95%CI: 84.7-89.0). Sensitivity was lowest at the first round (81.5%; 95%CI: 75.6-86.2), and increased to 91.9% (95%CI: 83.9-96.5) for subsequent rounds. Applying the Interval Cancer Proportion method, sensitivity was 83.9% (95%CI: 81.3-86.2), and it was highest at the first round (89.0%; 95%CI: 85.7-91.6), ranging between 73% and 83.1% at subsequent rounds.

CONCLUSIONS

A faecal immunochemical test sensitivity for cancer higher than 80% resulted in a low incidence of interval colorectal cancers, representing an accurate estimate of one of the major limits of screening programmes. Due to intrinsic biases, the Proportional Interval Cancer Rate and the Interval Cancer Proportion methods generated different trends in faecal immunochemical test sensitivity by screening round.

Benefits of switching from guaiac-based faecal occult blood to faecal immunochemical testing: experience from the Wallonia-Brussels colorectal cancer screening programme

Background

Faecal immunochemical tests (FITs) have replaced guaiac-based faecal occult blood test (gFOBTs) in several colorectal cancer (CRC) screening programmes. We aimed to evaluate the benefits of this transition based on the Wallonia–Brussels-organised CRC screening programme.

Methods

A total of 1,569,868 individuals aged 50–74 years, who were invited to screening during 2009–2017, were studied by linking their screening records with insurance, pathology and cancer data in the Belgian Cancer Registry. We compared neoplasm detection rates and positive predictive values (PPVs) of gFOBT and FIT at 15 µg haemoglobin per gram cut-off in screen-naive individuals. We furthermore examined the incidence rates of interval cancer in gFOBT- and FIT-based screening programme.

Results

Advanced neoplasms were detected less frequently by gFOBT (0.8%) than by FIT (1.3%), with a difference of 0.5% (P < 0.01). PPVs were lower for gFOBT (15.1%) than for FIT (21.7%) for advanced neoplasms (difference 6.6%, P < 0.01). Compared to participants with negative gFOBT, those with negative FIT were 77% less likely to develop interval cancer (incidence rate ratio 0.23, 95% confidence interval 0.16–0.33).

Conclusion

Our study demonstrated that in an organised CRC screening programme, replacing gFOBT with FIT improved neoplasm detection rate and substantially reduced interval cancer incidence.

Characteristics of Advanced Colorectal Cancer Detected by Fecal Immunochemical Test Screening in Participants with a Negative Result the Previous Year

BACKGROUND

There is sufficient evidence to show the mortality reduction effect of colorectal cancer (CRC) screening programs using the fecal occult blood test (FOBT). However, we see cases that are found to be advanced CRC despite yearly FOBT screening.

METHODS

The aim of this study was to investigate the characteristics of advanced CRC detected by a fecal immunochemical test (FIT) screening program in participants with a negative screening result the previous year, which we call "Negative advanced CRC". A total of 109,639 participants (10.0% required colonoscopy, of whom 76.9% received one) underwent a CRC screening program using a FIT from fiscal 2009 to 2017. Negative advanced CRC was compared with advanced CRC (First advanced CRC) found at the first visit in a person who had not had a FIT screening history for more than 3 years. In addition, we compared the characteristics of Negative advanced CRC with those of interval cancer: cancer cases detected after a negative screening result and before the date of the next recommended screening.

RESULTS

A total of 339 cases of CRC (175 male: 164 female, 173 early stage: 166 advanced stage) were detected in the nine-year CRC screening period. The rate of right-sided CRCs was significantly higher in female (P < 0.01), advanced stage (P < 0.01), negative result previous year (P < 0.01), and symptom-negative (P < 0.01) participants than in each counterpart, respectively. The ratio of female (22/35; 62.9%) patients in Negative advanced CRCs tended to be high compared with that (40/83; 48.2%) in First advanced CRCs (P = 0.145). Overall, 22 (62.9%) of 35 Negative advanced CRCs and 28 (33.7%) of 83 First advanced CRCs were located in the right-sided colon, and the rate was significantly higher in Negative advanced CRCs (P < 0.01). In addition, the frequency of female patients was significantly higher in right-sided Negative advanced CRCs than in right-sided First advanced CRCs (P = 0.03).

CONCLUSION

The characteristics of Negative advanced CRC cases (female and right-sided colon) were similar to those of interval cancer reported so far. In the future, it will be necessary to introduce a screening program that is highly sensitive to right-sided CRC.

Occurrence and characteristics of faecal immunochemical screen-detected cancers vs non-screen-detected cancers: Results from a Flemish colorectal cancer screening programme

BACKGROUND

Colorectal cancer (CRC) and its precursor lesions are detected at an early stage by CRC screening programmes, which reduce CRC-related mortality. An important quality indicator for CRC screening is the occurrence of interval CRC (IC) between screening rounds. Currently there is no guideline regarding acceptable levels of ICs in CRC screening programmes, and ICs reported in prior work vary considerably.

METHODS

This study describes the occurrence of screen-detected (SD) CRC and non-screen-detected CRC within the population-based CRC screening programme of Flanders, stratified by multiple variables such as sex, age, tumour location and tumour stage between October 2013 and July 2017. In addition, faecal immunochemical test (FIT) IC proportions over the sum of SD-CRCs and FIT-ICs are calculated, together with FIT sensitivity and programme sensitivity to display the effectiveness of detecting CRC by the screening programme.

RESULTS

Of 1,212,354 FIT participants, 4094 were diagnosed with SD-CRC, whereas 772 participants were diagnosed with CRC between FIT-screening rounds. Significant associations were shown between people not being SD for CRC and women, older individuals, right-sided tumour location and more advanced tumour stage. Furthermore, a clear distinction was shown between the right-sided and the left-sided colorectum concerning all above-mentioned variables and distributions of tumour stages.

CONCLUSION

The Flemish FIT-interval CRC proportion of 15.9% was within the limits of previously published results. In addition, calculations show that the effectiveness of the screening programme is dependent on tumour location, suggesting that future research should report results stratified by location.

The detection of interval colorectal cancers following screening by fecal immunochemical test may predict worse outcomes and prompt ethical concerns: a 6-year population-based cohort study in a full district

The rates of colorectal cancer (CRC) interval surveyed in screen-detected patients using a fecal immunochemical test (FIT) are not negligible. The aim of this study was to assess the effect of interval cancer on outcomes compared with a population with cancer diagnosed after a positive test result. All patients between 50 and 71 years of age, who were residents of the Mantua district, affected by CRC and operated on from 2005 to 2010 were reviewed. Other than patient-related, disease-related, and treatment-related factors and tumor location, this population was differentiated as either participating or not to screening and then into populations developing interval cancer after a negative FIT result. Mortality was investigated by univariate analysis and by overall survival rates. The mean age of the 975 patients enrolled was 62 years (61.7% males). Most patients (n=575, 59%) were not screen detected, and 400 (41%) were screen detected. Fifty-six (5.7%) patients in the latter group, representing 14% of the participants, developed interval cancer after a negative FIT result. Their cancer was mostly localized in the right colon (41.1%) instead of the left colon and rectum (P=0.02). They also showed higher stages (P=0.001), a moderate degree of differentiation (P=0.001), and overall higher mortality rates than patients with cancer diagnosed after a positive test result (P=0.001). The effect of interval CRC after screening with FIT resulted in worse outcomes compared with the FIT-positive group. With such findings, patients who had negative results for FIT should be informed of the risk of developing cancer within the rounds of screening to independently gain educational skills in the area of health prevention.

Participant-Related Risk Factors for False-Positive and False-Negative Fecal Immunochemical Tests in Colorectal Cancer Screening: Systematic Review and Meta-Analysis

OBJECTIVES

Colorectal cancer (CRC) screening using fecal immunochemical tests (FIT) may reduce CRC-related mortality but its effectiveness is influenced by the limited accuracy of FIT. Identifying individuals at increased risk of a false FIT result could improve screening, but the available evidence is conflicting. We performed a systematic review and meta-analysis on risk factors for false-positive and false-negative FIT results in CRC screening.

METHODS

A systematic search in MEDLINE, EMBASE, and Cochrane Library identified publications (before 29 January 2017) on risk factors (known at time of FIT invitation) associated with false FIT results (presence/absence of advanced neoplasia) in a CRC screening setting. Risk of bias was assessed using QUIPS. In meta-analysis, summary relative risk ratios and corresponding 95% confidence intervals were calculated for each risk factor.

RESULTS

Of 518 records identified, 14 studies with 54,499 participants in total were included for analysis. In meta-analysis, male sex was associated with a significantly lower risk of false-positivity (RR 0.84, CI 0.74-0.94), whereas participants using non-steroidal anti-inflammatory drugs (NSAIDs) had a higher risk (RR 1.16, CI 1.06-1.27). The use of anticoagulants was most frequently studied, without a significant effect on FIT positivity. Males (RR 1.83, CI 1.53-2.19), participants with a family history for CRC (RR 1.61, CI 1.19-2.15), hyperglycemia (RR 1.29, CI 1.02-1.65), hypertension (RR 1.50, CI 1.14-1.98), obesity (RR 1.38, CI 1.11-1.71), and (former) smokers (RR 1.93, CI 1.52-2.45) were all at significantly higher risk for false-negative results. Age was not found to have a systematic effect on either FIT false-positivity or false-negativity in meta-analysis.

CONCLUSIONS

Multiple risk factors, known at time of FIT invitation, are associated with false FIT results in CRC screening. This information can be used to identify populations risking false reassurance after a negative result or unnecessary colonoscopy after a positive result, and to further optimize CRC screening effectiveness.

Interval cancers after negative immunochemical test compared to screen and non-responders' detected cancers in Slovenian colorectal cancer screening programme

Background

We assessed the incidence and characteristics of interval cancers after faecal immunochemical occult blood test and calculated the test sensitivity in Slovenian colorectal cancer screening programme.

Patients and methods

The analysis included the population aged between 50 to 69 years, which was invited for screening between April 2011 and December 2012. The persons were followed-up until the next foreseen invitation, in average for 2 years. The data on interval cancers and cancers in non-responders were obtained from cancer registry. Gender, age, years of schooling, the cancer site and stage were compared among three observed groups. We used the proportional incidence method to calculate the screening test sensitivity.

Results

Among 502,488 persons invited for screening, 493 cancers were detected after positive screening test, 79 interval cancers after negative faecal immunochemical test and 395 in non-responders. The proportion of interval cancers was 13.8%. Among the three observed groups cancers were more frequent in men (p = 0.009) and in persons aged 60+ years (p < 0.001). Comparing screen detected and cancers in non-responders with interval cancers more interval cancers were detected in persons with 10 years of schooling or more (p = 0.029 and p = 0.001), in stage III (p = 0.027) and IV (p < 0.001), and in right hemicolon (p < 0.001). Interval cancers were more frequently in stage I than non-responders cancers (p = 0.004). Test sensitivity of faecal immunochemical test was 88.45%.

Conclusions

Interval cancers in Slovenian screening programme were detected in expected proportions as in similar programmes. Test sensitivity was among the highest when compared to similar programmes and was accomplished using test kit for two stool samples.

Interval Colorectal Cancer Incidence Among Subjects Undergoing Multiple Rounds of Fecal Immunochemical Testing

BACKGROUND & AIMS

Among subjects screened for colorectal cancer (CRC) by the guaiac fecal occult blood test, interval cancers develop in 48% to 55% of the subjects. Data are limited on how many persons screened by fecal immunochemical tests (FIT), over multiple rounds, develop interval cancers. In the Netherlands, a pilot FIT-based biennial CRC screening program was conducted between 2006 and 2014. We collected and analyzed data from the program on CRCs detected during screening (SD-CRC) and CRCs not detected within the screening program (non-SD-CRC; such as FIT interval cancers, colonoscopy interval cancers, and cancer in nonparticipants).

METHODS

Screenees with a negative FIT result received a letter explaining that no blood had been detected in the stool sample and were re-invited, if eligible, for screening biennially. Screenees with a positive FIT result (hemoglobin concentration of 10 μg Hb/g feces) were invited for consultation and scheduled for colonoscopy; results were collected. After the fourth round of FIT screening, the cohort was linked to the Netherlands Cancer Registry, through March 31, 2015; participant characteristics, data on tumor stage, location (at time of resection), and survival status were collected for all identified CRC cases. A reference group comprised all persons with CRC diagnosed in the Netherlands general population during the same period, in the same age range (50-76 years), who had not been offered CRC screening. The median time between invitations (2.37 years) was used as a cutoff to categorize participants within the FIT interval cancer category. We compared participant characteristics, tumor characteristics, and mortality among subjects with SD-CRC and with non-SD-CRC.

RESULTS

A total of 27,304 eligible individuals were invited for FIT screening, of whom 18,716 (69%) participated at least once. Of these, 3005 (16%) had a positive result from the FIT in 1 of the 4 screening rounds. In total, CRC was detected in 261 participants: 116 SD-CRCs and 145 non-SD-CRCs (27 FIT interval cancers, 9 colonoscopy interval cancers, and 109 CRCs in nonparticipants). The FIT interval cancer proportion after 3 completed screening rounds was 23%. Participants with SD-CRC had more early-stage tumors than participants with non-SD-CRCs (P < .001). Of persons with SD-CRC and FIT interval cancers, significantly higher proportions survived (89% and 81%, respectively) compared with persons with colonoscopy interval cancers (44% survival) and nonparticipants with CRC (60% survival) (P < .001).

CONCLUSIONS

In an analysis of data from a pilot FIT-based biennial screening program, we found that among persons screened by FIT, 23% developed FIT interval cancer. FIT therefore detects CRC with 77% sensitivity. The proportion of FIT interval cancers in FIT screening appears to be lower than that with guaiac fecal occult blood testing. Clinical trial registry: yes, www.trialregister.nl, trial number: NTR5385.

Faecal occult blood testing screening for colorectal cancer and 'missed' interval cancers: are we ignoring the elephant in the room? Results of a multicentre study

AIM

Biennial faecal occult blood testing (FOBT) is used to screen for colorectal cancer throughout the UK. Interval cancers are tumours that develop in patients between screening rounds who have had a negative FOBT. Through a multicentre study, we compared the demographics of patients with interval cancers, FOBT screen detected cancers and cancers that developed in patients who chose not to participate in the screening programme.

METHOD

Five hundred and sixteen colorectal cancers were detected in the screening age group (60-74 years) population in three UK National Health Service hospitals over 2 years. One hundred and twenty seven (25%) were interval cancers, 161 (31%) were screen detected and 228 (44%) were cancers that developed in patients who had declined FOBT. The interval cancer group had a higher incidence of right-sided cancers (38% vs 29% and 24%), a higher proportion of high tumour stages (Dukes C and D) (70% vs 53% and 33%) and a shorter time from diagnosis to death (10 months vs 13 months and 24 months) compared to patients who had declined the FOBT and the FOBT screen detected cancers. Of all the patients studied, those with right-sided interval cancers had the worst outcome.

CONCLUSION

A quarter of the colorectal cancers diagnosed in our study were interval cancers. Patients with right-sided interval cancers had the highest proportion of Dukes C and D tumours coupled with the shortest survival time after diagnosis compared with the other groups.

Colorectal and interval cancers of the Colorectal Cancer Screening Program in the Basque Country (Spain)

AIM

To assess proportions, related conditions and survival of interval cancer (IC).

METHODS

The programme has a linkage with different clinical databases and cancer registers to allow suitable evaluation. This evaluation involves the detection of ICs after a negative faecal inmunochemical test (FIT), interval cancer FIT (IC-FIT) prior to a subsequent invitation, and the detection of ICs after a positive FIT and confirmatory diagnosis without colorectal cancer (CRC) detected and before the following recommended colonoscopy, IC-colonoscopy. We conducted a retrospective observational study analyzing from January 2009 to December 2015 1193602 invited people onto the Programme (participation rate of 68.6%).

RESULTS

Two thousand five hundred and eighteen cancers were diagnosed through the programme, 18 cases of IC-colonoscopy were found before the recommended follow-up (43542 colonoscopies performed) and 186 IC-FIT were identified before the following invitation of the 769200 negative FITs. There was no statistically significant relation between the predictor variables of ICs with sex, age and deprivation index, but there was relation between location and stage. Additionally, it was observed that there was less risk when the location was distal rather than proximal (OR = 0.28, 95%CI: 0.20-0.40, P < 0.0001), with no statistical significance when the location was in the rectum as opposed to proximal. When comparing the screen-detected cancers (SCs) with ICs, significant differences in survival were found (P < 0.001); being the 5-years survival for SCs 91.6% and IC-FIT 77.8%.

CONCLUSION

These findings in a Population Based CRC Screening Programme indicate the need of population-based studies that continue analyzing related factors to improve their detection and reducing harm.

Incidence of interval cancers in faecal immunochemical test colorectal screening programmes in Italy

Objective

In Italy, colorectal screening programmes using the faecal immunochemical test from ages 50 to 69 every two years have been in place since 2005. We aimed to measure the incidence of interval cancers in the two years after a negative faecal immunochemical test, and compare this with the pre-screening incidence of colorectal cancer.

Methods

Using data on colorectal cancers diagnosed in Italy from 2000 to 2008 collected by cancer registries in areas with active screening programmes, we identified cases that occurred within 24 months of negative screening tests. We used the number of tests with a negative result as a denominator, grouped by age and sex. Proportional incidence was calculated for the first and second year after screening.

Results

Among 579,176 and 226,738 persons with negative test results followed up at 12 and 24 months, respectively, we identified 100 interval cancers in the first year and 70 in the second year. The proportional incidence was 13% (95% confidence interval 10–15) and 23% (95% confidence interval 18–25), respectively. The estimate for the two-year incidence is 18%, which was slightly higher in females (22%; 95% confidence interval 17–26), and for proximal colon (22%; 95% confidence interval 16–28).

Conclusion

The incidence of interval cancers in the two years after a negative faecal immunochemical test in routine population-based colorectal cancer screening was less than one-fifth of the expected incidence. This is direct evidence that the faecal immunochemical test-based screening programme protocol has high sensitivity for cancers that will become symptomatic.

Interval cancers in a guaiac-based colorectal cancer screening programme: Consequences on sensitivity

Objective

To evaluate interval cancers in the population-based colorectal cancer screening programme of Stockholm/Gotland, Sweden.

Methods

From 2008, individuals aged 60–69 were invited to colorectal cancer screening using biennial guaiac-based faecal occult blood test (Hemoccult®). Interval cancers, defined as colorectal cancer among participants not diagnosed by the screening programme but registered in the Swedish cancer register, were evaluated by cross-checking the screening histories for all cancers in the region 2008–2012.

Results

Of 203,848 individuals from nine different birth cohorts who participated (∼60%), 4530 (2.2%) tested positive. All invited individuals were followed up for 24 months after invitation. The cancer register reported 557 colorectal cancer, 219 (39.3%) screen-detected cancers and 338 (60.7%) interval cancers, generating both test- and episode sensitivities of approximately 40% and an interval cancer-rate of 17.1/10,000 tests. Among individuals with positive tests without colorectal cancer diagnosed at work-up colonoscopy, 37 interval cancers (10.9%) occurred. There was statistically significant lower sensitivity in women, ranging 22.4–32.2%, compared with 43.2–52.0% in men. Age-group and tumour location were not strongly correlated to screen-detected cancer rates. The programme sensitivity increased by year (20.3–25.0%), with successively more colorectal cancers diagnosed within the expanding programme (11.6–16.2%).

Conclusion

Interval cancer is a quality indicator of a screening programme. As the interval cancer-rate determined in a well-organized population-based screening programme was actually higher than the screen-detected cancer rate, a change to a more sensitive screening test is indicated. The lower screen-detected cancers among women, and compliance and quality of work-up colonoscopies also need attention.

Interval cancers in a national colorectal cancer screening programme

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.