A review of clinical research on using FIT screening for colorectal cancer

ZENG Fan, CHEN Chen, HUANG Shi-mei, ZHANG Da-ya, BAI Fei-hu

1. Hainan Medical University, Haikou 571199, China

2. The Second Affiliated Hospital of Hainan Medical University, Haikou 570216, China

3. The Gastroenterology Clinical Medical Center of Hainan Province, Haikou 570216, China

Keywords:

ABSTRACT Colorectal cancer (CRC) has become the third most common cancer in the world and the second leading cause of death related to cancer.early screening of CRC can reduce its incidence rate and mortality.With the development of fecal immunochemical testing (FIT), FIT has been an important tool for screening CRC patients in high-risk groups worldwide.With the development of FIT, FIT has been an important tool for screening CRC patients in high -risk groups worldwide.In this paper, we describe the research progress of FIT screening for CRC.

Colorectal cancer ( CRC) is one of the most common tumors worldwide, with incidence and mortality rates increasing every year[1] , it is the third leading cause of cancer deaths worldwide and is considered a global public health problem[1].Early detection strategies for cancer as well as preventive measures are key to improving survival rates.Although colonoscopy is the gold standard for CRC screening[2] , screening with colonoscopic confirmation in patients with positive results after primary screening for CRC using stool immunochemical testing is widely advocated by many screening programs worldwide[3].

Compared to the traditional guaiac fecal occult blood test (gFOBT),fecal immunochemical testing (FIT) is easy to perform, sensitive and does not require dietary restrictions.priority investigation and is superior to symptom assessment alone in identifying colorectal cancer[4-5].Its quantitative nature optimizes the use of resources.FIT has been proposed as an exclusion test for colorectal cancer[5].This article provides an overview of the epidemiology of CRC,the principles of the FIT test, its screening efficacy for CRC, and summarizes and outlines the factors that influence the efficacy of the FIT screen, the advantages and disadvantages of the FIT screen and its innovative applications, and provides an outlook on the future use of the FIT screen for CRC.

1.CRC Overview

CRC is a malignant tumor that occurs in the mucosal epithelium of the colon and rectum.The incidence of CRC in different parts of the body is, in descending order, rectum, sigmoid colon, cecum,ascending colon, descending colon, and transverse colon; CRC is insidious, asymptomatic or asymptomatic in early stages, with only abdominal discomfort, etc.The early diagnosis rate is only 5%, and 60%-70% of patients are diagnosed with CRC in the middle and late stages[6].

CRC generally takes 5-10 years to progress from precancerous lesions to cancer, which provides an important window of time for early diagnosis and clinical intervention, and is one of the most suitable cancers for early screening and prevention[7-8].In a European study, the risk of developing CRC in people who were screened for CRC decreased from 1.22% to 0.84% after 10 years[9].Studies of relevant CRC screening trials all point to a sustained reduction in CRC mortality and a significant reduction in all-cause mortality with CRC screening[8-11].Thus, early screening is effective in reducing the incidence of CRC and its mortality.

2.FIT

2.1 FIT test principle

Fecal occult blood test (FOBT) is a simple, safe and inexpensive method to screen for colorectal cancer, which can be divided into gFOBT and FIT[12].

FOBT can detect small amounts of blood in the stool, which may indicate intestinal bleeding[13].In case of malignant disease bleeding is continuous, while in presence of benign bleeding conditions such as ulcers it is intermittent, thus allowing differentiation between benign and malignant disease.

FIT is an anti-human hemoglobin antibody that binds to the hemoglobin antigen in the stool to form an antigen-antibody complex producing a specific chemical reaction, and can reliably measure the hemoglobin concentration in stool (f-Hb) by immunoassay to the nearest microgram of Hb per gram of stool (μg/g)[14].

2.2.Common clinical FIT assay types

The types of FIT commonly used in clinical practice are qualitative and quantitative FIT, both of which are based on the principle of antigen-antibody reaction.The qualitative method separates soluble Hb from feces by lateral flow immunochromatography and is captured by human Hb antibodies and made visible by various visualization techniques[14].Quantitative FIT uses an immunoemulsion agglutination method to detect trace amounts of Hb in stool with high sensitivity of antigen-antibody reaction[13].Related studies have found that quantitative FIT is superior to qualitative FIT in CRC screening in terms of improving the detection of advanced tumors and reducing the workload of colonoscopy[15,16].

FIT is mainly divided into colloidal gold, enzyme-linked immunosorbent assay and monoclonal antibody assay.The colloidal gold method is the most commonly used immunoassay for fecal occult blood testing and is mainly used to detect human hemoglobin or transferrin antigen by immunoassay strips, which is more sensitive, specific and accurate than chemical methods and is recommended by the World Health Organization and the World Association of Gastrointestinal Screening[17]

2.3 Superiority of the FIT test for screening colorectal cancer

2.3.1 Diagnostic efficacy of FIT

The diagnostic efficacy of FIT is higher than that of gFOBT and has become the main fecal occult blood test for colorectal cancer screening in the population.fIT has replaced g FOBT because of its ease of use, quantitative analysis, and higher sensitivity for advanced colorectal neoplasms (ACN)[6-30].

Compared to the FIT test,gFOBT is less sensitive and the results are susceptible to external factors such as diet and drugs[25].In the last two decades, countries have increasingly adopted FIT kits over gFOBT because of their superior sensitivity and specificity[31].Unlike gFOBT, the FIT kit cannot detect upper GI bleeding due to the breakdown of lower GI hemoglobin and is not affected by upper GI bleeding[28].

In a study by Akram et al, FIT and gFOBT were applied separately for CRC screening in the population and found significantly higher CRC detection rate in the FIT group (0.79% vs 0.8%, P = 0.003)with higher sensitivity and specificity[31].Cai Jinping et al.applied FIT and gFOBT for early CRC screening in 50 patients suspected of having early colorectal cancer, respectively, and confirmed that FIT was more effective in early CRC screening[30].In a metaanalysis, the sensitivity of CRC diagnosis was found to be about 70-80% when the FIT kit was applied for screening[33-35], and Mikaël et al.applied FIT for CRC screening and found its sensitivity to be 80.5% for CRC diagnosis[36].Therefore, a combination of the above studies found that compared to gFOBT, FIT is more sensitive in the screening process of CRC, which well circumvents the disadvantages of gFOBT such as the tendency of false positives and false negatives,low sensitivity, and susceptibility to external factors such as diet, and its screening efficacy in CRC screening is higher.

2.3.2 Appropriate positive thresholds can improve the diagnostic efficacy of FIT

FIT has been widely used for screening, with an estimated sensitivity of 90% for a single low-threshold FIT.Nigel et al.demonstrated in their study that FIT can be used to rule out early CRC in symptomatic patients who meet the criteria with a sensitivity equivalent to colonoscopy[5].Emily et al.found that lowering the FIT threshold ( 10 μg/g) increased the detection rate of advanced tumors,but the proportion of patients requiring diagnostic colonoscopy would be doubled.If annual low-threshold FIT were implemented instead of triennial colonoscopy, the number of colonoscopies could be reduced by more than 70%, with significant cost savings[37].In a 2017 UK National Institute for Health and Clinical Excellence(NICE) study analyzing the diagnostic accuracy of FIT screening for CRC, when the FIT test threshold was gradually increased from 10 μg/g to 20 μg/ g, the pooled estimated sensitivity increased from 89.1% to 89.5% and specificity increased from 85.8% to 86.6%[38].Therefore, appropriate adjustment of the FIT test threshold can effectively improve its diagnostic efficacy.

2.3.3 Effect of FIT test on morbidity and mortality of CRC

FIT for planned screening helps to reduce the morbidity and mortality of CRC in the screened population[2,39].For example, Han-Mo Chiu et al.applied FIT for CRC screening in Taiwan province and found a 34% reduction in late CRC incidence and 40% reduction in mortality after screening[40].Similarly, in a study in Texas, FIT combined with colonoscopy was found to have a significantly higher detection rate of adenomas than colonoscopy alone[41].Zhao S, Wang S et al.formed a risk stratification model (Li’s model) based on the Chinese Colorectal Polyp Care (NCPC) score together with FIT that was able to identify 55.8% of advanced adenomas and 72.7% of early CRC.this model is expected to be a feasible risk stratification method to improve the efficiency of colonoscopy[42].Therefore, the application of FIT test for screening CRC can reduce its morbidity and mortality to a certain extent, and is a screening tool with high screening efficacy, which deserves to be recommended as one of the common tools for early screening of CRC.

2.4.Factors affecting the efficacy of FIT screening

2.4.1 Effect of positive threshold on FIT screening efficacy

Farah K et al.applied FIT screening for CRC and found that when setting the FIT threshold at 4 μg Hb/g, it had a positive predictive value of 5.0%, a negative predictive value of 99.8%, and a polyp detection rate of 25.5% for the diagnosis of colorectal cancer.When the FIT threshold was adjusted to 10 μg Hb/g, CRC and polyp detection rates were increased[43].Similarly, a study applying FIT screening for CRC in the Herts Valley noted a sensitivity of 93%,91% and 72% when the FIT threshold was 4 μg Hb/g, 10 μg Hb/g and 100μg Hb/g, respectively[44].Gerrard et al.found that increasing the FIT threshold from 10 μg Hb/g to 20μg Hb/g,which increased the annual rate of missed CRC[45], the annual mean(NNI) of missed CRC increased significantly; therefore, 10 μg Hb/g seems to be the optimal threshold for detecting CRC in a dual FIT strategy[45].Therefore, when different positive thresholds are set for FIT, their diagnostic efficacy in screening for CRC is different.Only when FIT sets appropriate thresholds, its detection rate and sensitivity of screening for CRC can achieve optimal results.In the current studies, it can be found that a FIT threshold of 10 μg Hb/g is used to achieve a high CRC detection rate and screening sensitivity.However, in these studies, the specificity results for different thresholds of FIT were few, and future studies could focus more on its diagnostic specificity.

2.4.2 Effect of gender and age on the efficacy of FIT screening

Mikaël[36] and others found higher sensitivity in men (83.7%) than women (76.2%; P=0.066) in FIT screening for CRC, yet it was not affected by the age of the subjects.Another study found that males were more sensitive than females in FIT screening for CRC.Similarly, a study that applied FIT to screen for CRC and studied its sensitivity in Spain noted a higher rate of positivity and positive predictive value in men than in women[45].

Some studies have shown that age does not make a significant difference in the sensitivity of FIT screening for CRC, and its sensitivity even decreases with increasing age[46,47].One study reported the sensitivity and specificity of detecting CRC and did not find significant differences in test performance between younger and older populations[47].Thus, in FIT screening for CRC, FIT has a higher diagnostic sensitivity for men than for women, with little difference in diagnostic sensitivity between different age groups.Although the above study finally concluded the influence of gender and age on the diagnostic efficacy of FIT, the specific mechanism of influence has been rarely reported, so the future research in this area is promising and worthy of deeper investigation.

2.4.3 Effect of different sites and stages of CRC development on the screening efficacy of FIT

It was found that the screening sensitivity of FIT for distal CRC was significantly higher than that for proximal colon cancer (94.2%vs 71.1%, P<0.001).And the screening sensitivity of applying FIT to screen different stages of CRC, such as stage I, II, III and IV, was 89.6%, 88.7%, 83.3%, 71.2% and 68.3%, respectively (P<0.001) [36].the earlier the stage of CRC development, the higher the sensitivity of FIT.

It has been found that CRC occurring in the right colorectum is usually more aggressive, with earlier onset of clinical symptoms, and therefore may be diagnosed more quickly than CRC occurring in the left colorectal site[49].Others have found that FIT is more sensitive for screening distal CRC than proximal[50], and they suggest that the difference in FIT screening sensitivity may be caused by different intracellular Hb transport and degradation times at different sites of CRC occurrence; it has also been suggested that it is caused by the different locations of CRC occurrence, where Hb has different electrical potential and mechanical stress[53].Overall, FIT sensitivity is higher in early CRC than in late CRC.this difference has long been observed in previous studies[49-53].

As mentioned above, FIT is more sensitive for screening distal CRC than proximal CRC, and the exact mechanism is subject to debate, but with this pattern it is expected to identify the location of tumorigenesis early in future early screening for CRC to facilitate the determination of specific treatment options.Moreover, the sensitivity of FIT for early CRC screening is higher than that of late CRC, which is very beneficial for early screening of CRC.

2.4.4 Effect of the number of FIT screening on screening efficacy

There are a number of studies on the effect of the number of FIT screens for CRC on screening efficacy, with varying results.In a study of screening for CRC in a dual FIT cohort, the sensitivity of performing two FIT screens for CRC was found to increase from 93.3% to 96.6%, and the rate of missed tests was reduced by half.And dual testing would increase the number of investigations by 7.3% compared to a single testing method.The trade-off between reduced missed pathology and a modest increase in workload suggests that dual testing may be worthwhile[44].A Norwegian study applying FIT nationally to screen for CRC every two years for up to four times found that the detection rate of CRC and advanced tumors increased with increasing rounds of FIT screening[49].Meanwhile,Clark Gavin et al.found that the difference between the second and first f-Hb percentile was highly statistically significant (P<0.001)in a population that applied FIT screening for CRC in two rounds,and that performing two rounds of screening improved the detection rate of advanced adenomas[50].Another Meta-analysis noted that the number of FIT screenings was not significantly associated with most indicators, except for the participation rate of the screened population[51].Combining these findings and based on the fact that two FIT screenings did not significantly increase clinical benefit, the current application of the FIT screening CRC program still recommends one FIT screening per round.

3.FIT screening for colorectal cancer has some limitations

3.1 The participation rate of FIT screening for CRC is not yet high

In a Meta-analysis by Ding Hanyue et al.it was found that studies with larger sample sizes reported lower participation rates (sample size <50,000: 67.53%, 50,000-500,000: 48.79%, >500,000: 45.37%,P=0.005;); and it was noted that the worldwide application of FIT screening for CRC population participation rates varied by location,with 55.25% in Asia Pacific, 52.72% in Europe, 45.57% in North America, and 90.19% in South America[49].

In China, the participation rate of colonoscopy screening is only 14%, and the national awareness of the importance of colorectal cancer screening in China is still relatively lacking due to insufficient publicity, and the overall participation rate of FIT screening for colorectal cancer in China is still low[52].

3.2 Low adherence of patients with positive FIT results to colonoscopy follow-up

Although FIT has been found to increase participation rates in CRC screening to some extent, insufficient attention to positive FIT results, lack of awareness of CRC, and lack of significant physical discomfort in the current screening population are the main reasons affecting compliance with colonoscopy in high-risk groups, and untimely additional colonoscopies can ultimately lead to delayed disease[53,54].

In an observational study, only 76.0% (range: 12.5%～96.7%)of FIT-positive subjects attended the recommended colonoscopy.Another study found that only 39.8% of high-risk individuals in the Shanghai, China, population participated in colonoscopy follow-up,while compliance was as low as 24.0% in the Pudong New Area,Shanghai, where only 30.4% of FIT-positive subjects participated in colonoscopy[55].

3.3 There are many factors affecting the accuracy of FIT screening for CRC

However, there are still limitations of FIT screening for CRC, for example, a study in Nanchang noted that for CRC with intermittent bleeding, three consecutive days of testing are required, or for early CRC without bleeding, colorectal lesions cannot be screened[56,57].Therefore, when performing early CRC screening, it is important not to rely only on FIT results, but also to combine with clinical symptoms, imaging and serology to improve accuracy[31].And a study in Guangzhou found that the FIT test only used a qualitative method and not a quantitative method, and the Hb content in stool has a critical role in determining the results of colonoscopy, which can easily confound the results of the study[47].

The commonly used FIT test is less sensitive for precancerous lesions (12.3～32.4%) and early cancers (40%)[63].In addition, FIT tests may show false-negative results due to smoking or advanced age, both of which are well-known risk factors for CRC, leading to some cases being missed.

4.Innovative application of FIT: multi-target fecal FIT-DNA technique

FIT has the advantages of being noninvasive, simple, and inexpensive by detecting hemoglobin in stool to determine whether there is bleeding, but the biggest drawback is that it is prone to false positives and false negatives and has low specificity[64].Therefore,there are still limitations in applying FIT to screen for CRC.

In January and April 2021, an innovative application of FIT-multitargeted fecal FIT-DNA technology was selected as the first Chinese colorectal cancer prevention and treatment guideline initiated by the National Cancer Center and the Chinese Society of Clinical Oncology (CSCO) colorectal cancer treatment guideline, becoming the only bowel cancer screening genetic testing technology selected in national guidelines[65].

Multi-target fecal FIT-DNA testing is a laboratory technique to detect DNA mutations in fecal exfoliated cells and combine FIT to form an individual composite risk score (combined FIT, fecal KRAS, BMP3 methylation, NDRG4 methylation, and β-actin),and subjects whose composite score exceeds a preset threshold are defined as high-risk and need to undergo colonoscopy[66 ].

A meta-study found[64] that FIT-DNA screening for CRC had a combined sensitivity of 94%, a combined specificity of 91%, and a combined diagnostic ratio of 142.FIT-DNA screening for patients with progressive adenoma had a combined sensitivity of 50%, a combined specificity of 90%, and a combined diagnostic ratio of 10.This indicates that FIT-DNA has a high detection rate for CRC.FIT-DNA has a certain detection rate for patients with progressive adenoma, and there is a certain rate of underdiagnosis but a low rate of misdiagnosis for both CRC and screening of patients with progressive adenoma.

Y L Li et al[67] found that the sensitivity of FIT-DNA testing for early colorectal cancer and advanced adenoma was 7/7 and 8/12, respectively, by grouping and comparing patients with first diagnosed but untreated CRC with those with CRC in the intervention group.the negative predictive value was 98.1%(104/106) and 93.7% (104/111), respectively.The overall screening sensitivity for both early colorectal cancer and advanced adenoma was 15/19 and the negative predictive value was 96.3% (104/108).the diagnostic sensitivity of the FIT-DNA test for colorectal cancer was 98.8% (85/86) and for advanced adenoma was 8/12.the overall diagnostic sensitivity and specificity of the FIT-DNA test after inclusion in the intervention group were 91.6% (98/107) and 89.1%(114/128).This indicates that the FIT-DNA test has a high early screening and diagnostic effect on colorectal cancer.This indicates that overall FIT-DNA has a very high value in diagnosing colorectal cancer and progressive adenoma.

The results of Clear-C, the first prospective large-scale multicenter clinical registry trial I for early cancer screening in China, at the 2020 CSCO Annual Meeting, suggest that the combined multi-target fecal FIT-DNA test has a detection sensitivity of 95.5% and 63.5%for colorectal cancer and progressive adenoma, respectively, and a negative predictive value of 99.6% for colorectal cancer[64].

Therefore, in general, FIT-DNA compensates for the shortcomings of FIT, which is prone to false positives and false negatives and low specificity, and is a very ideal screening index, but the clinical value is still controversial due to the lack of clinical trial data in China at present.However, due to the lack of clinical trial data in China, the clinical value is still controversial.With the continuous clinical trial research of the multi-targeted fecal FIT-DNA combination test, the application of this technology for early screening of CRC is still very promising.

5.Summary and Outlook

By screening with FIT, CRC morbidity and mortality can be reduced to a certain extent and CRC detection rate can be improved.The main problems of FIT at present are the poor compliance of participants and the fact that it is mainly used for large-scale population screening and cannot be individualized for some populations.In the future, it is expected that the positive threshold of the FIT test can be flexibly changed and the flexibility of the test can be increased to further improve the superiority of FIT for CRC screening and to develop innovative FIT.

Authors’ Contribution

Zeng Fan: wrote the paper and revised it; Chen Chen, Huang Shimei, and Zhang Daya were responsible for collecting literature and participated in part of the writing; Bai Feihu proposed revisions and reviewed the article.

No potential conflicts of interest were identified by all authors during the study.