A New-Generation Fecal Immunochemical Test (FIT) Is Superior to Quaiac-based Test in Detecting Colorectal Neoplasia Among Colonoscopy Referral Patients

Discussion

In principle, screening of CRC can provide possibilities for both i) the primary prevention (i.e., finding pre-cancerous adenomas that could later undergo malignant transformation) and ii) the secondary prevention (detecting early cancers that can be more effectively treated) (6-9). Until now, however, the impact of CRC screening by the conventional quaiac-based FOB tests (19, 20) has been doubtful. Indeed, a recent meta-analysis of the ongoing FOB test screening trials indicated no benefit for all-cause mortality (RR=1.00, 95%CI=0.99-1.03) (5, 10), strongly challenging the efficacy of CRC screening by conventional FOB testing (6, 7). In this respect, the new FIT tests seem more promising. When compared to, the quaiac tests in head-to-head settings (12-15, 17) and in a randomized controlled trial (RCT) (16), FIT tests proved to be superior to the quaiac tests in detecting any type of colorectal neoplasia (6, 7).

The accumulated literature on FIT tests was recently subjected to meta-analysis by Lee at al. (21). Out of the 53 available studies, 18 were found to be eligible for this formal meta-analysis, fulfilling all the inclusion criteria (9, 22-38). Accordingly, the pooled SE, SP, positive likelihood ratio and negative likelihood ratio of FITs for CRC detection were: 0.79 (95%CI=0.69-0.86), 0.94 (CI=0.92-0.95), 13.10 (CI=10.49-16.35) and 0.23 (CI=0.15-0.33), respectively, with an overall diagnostic accuracy of 95% (95%CI=93%-97%). There was a substantial heterogeneity between the studies in both the pooled SE and SP estimates (21). Interestingly, a single-sample FIT had similar SE and SP as multiple-sample testing, independent of the FIT brand. Unfortunately, the authors decided to conduct their meta-analysis using the CRC as the only study endpoint, mainly because of the substantial heterogeneity in the reporting practices of adenomas in different studies (21). Biohit ColonView quick test, as a newcomer (in 2014) in the field, was not among the FIT brands included in this meta-analysis.

The present study reports a direct (head-to-head) comparison of the new ColonView quick test and the leading FOB test (HemoccultSENSA) in the colonoscopy referral setting. Importantly, we preserved the option for any patient who felt unsecure or clearly non-compliant with the instructions of HemoccultSENSA sampling to refrain from sampling for this test and only submit the ColonView sample. Although potentially compromising the patient compliance, this approach offers an advantage for comparing these two tests without bias caused by the non-compliant dietary and medication restrictions inherent to all guaiac-based FOB tests (6, 7, 15, 16, 19, 20).

For all three study endpoints, CV is a more sensitive test, while HS is a more specific one (Table II). The small superiority in SP does not compensate the marked inferiority in SE of HS, however, which makes CV a clearly superior test in detecting A and A/AC endpoints (p=0.0001). The same applies to both the visual and automatic reading of the CV test, which give practically identical results. This difference in clinical performance of the two tests is clearly due to their different analytical sensitivity. CV, as a more sensitive test, detects practically all cases of occult blood (>95%), while HS, with a lower analytical sensitivity, misses 70% of the adenomas, >40% of the A/AC combined endpoint and 15% of AC cases. On the other hand, HS is more specific to all these neoplastic causes of FOB as these calculations (Table II) include all causes of bleeding and most of the non-neoplastic causes remain below the threshold of HS, although ranking (false-) positive with the CV test. Due to this very same reason, the PPV of HS to all neoplastic causes of FOB is higher than that of CV, which predicts occult blood due to any cause. In CRC screening, a sensitive test is preferred, however, because all occult blood is abnormal and important to detect. On the other hand, a test with low SE is a disadvantage because of the real danger of missing a substantial proportion of clinically important colorectal neoplasia (6, 7, 9, 12-17).

There is published evidence that detection of the Hb/Hp complex displays a significantly increased sensitivity in recognition of colorectal neoplasia, compared to the Hb detection (15, 39). This observation has a solid foundation in the known metabolism of the Hb molecule in any extra-vascular blood, FOB included. The Hb molecule consists of 2 pairs of peptide (α- and β-globins) chains and 4 heme groups, each with one atom of iron. Free Hb may separate into α-β molecules, which are bound to a protein called haptoglobin (Hp). This Hb/Hp complex plays an important role in the retrieval of Hb from the lysed erythrocytes and, importantly, this complex is very stable resisting acid and proteolytic degradation. This means that the Hb/Hp complex can be detected even after longer passage through the bowel, thus increasing the chance that also the blood derived from proximal adenomas and carcinomas (and even from the stomach) can be detected in the stool sample (15, 39). Out of the two tests compared here, HS is based on Hb detection alone, while CV detects both Hb and Hb/Hp complex. Thus, the mere demonstration of a significantly higher SE of the CV test (Table II) provides indirect confirmatory evidence to substantiate this observation of Sieg et al. (15) and Lüthgens et al. (39).

To provide direct evidence that detection of the Hb/Hp complex is superior to Hb alone, the performance indicators of our CV test were analyzed separately for its Hb and Hb/Hp components (Table III). The results are straightforward. For the adenoma endpoint, the Hb/Hp complex is 15% more SE than Hb alone and this difference is still 8% for the A/AC endpoint, but disappears for the AC endpoint. This is most likely explained by a more profuse leading from the malignant lesions, being detectable equally by Hb and Hb/Hp complex. This superior sensitivity of the Hb/Hp complex -as compared to Hb alone-becomes more accentuated when the lesions are stratified into proximal and distal tumors (A/AC endpoint) (Table IV). Exactly as suggested (15, 39), the Hb/Hp complex remains stable over the entire course of the large bowel in contrast to Hb, which is degraded on the way and remains undetectable both by HS and the Hb component of the CV test. Indeed, HS and Hb component of the CV test perform equally poorly in detection of proximal colon tumors, with no statistical significance in the AUC comparison test (p=0.426 and p=0.258 for VR- and AR-mode, respectively) (Table IV). The difference is dramatic when Hb/Hp detection is used; all proximal colon tumors are invariably detected (SE=100%). In these calculations, all non-neoplastic causes of FOB were excluded, to test the detection accuracy for the neoplastic lesions. This is in sharp contrast to the Hb testing alone, showing SE of 41.2% and 52.9% in the HS and CV test, respectively. These observations imply that, to be highly effective, a FIT test can be based on detection of the Hb/Hp complex alone, with no need to include the Hb component in the test.

Not unexpectedly, this difference between Hb and Hb/Hp complex is less dramatic for the distal colon tumors. Even HS performs markedly better in distal than in proximal tumors (AUC comparison, p=0.0646) but the difference to the CV test remains still highly significant (p=0.0001 for almost all settings). This includes also the comparison between HS and the Hb component of CV, with the latter being almost 30% more sensitive for distal tumors (65.5% vs. 92.0%). In this setting, where all non-neoplastic causes of FOB were excluded, also the differences in test specificity (shown in Table II) between HS and CV disappear completely confirming the above notions to explain the reason for this higher specificity of HS in settings where all causes of FOB are included. Thus, the only reason for the inferior sensitivity of HS -as compared to CV in both proximal and distal colon tumors- must reside in the lower analytical sensitivity of the former, leading to a significant proportion (almost 60% at worst) of false-negative results. Missing almost 60% of the proximal colon tumors (A/AC) and even 35% of those in the distal colon, should invalidate the use of HemoccultSENSA as an acceptable CRC screening test (6, 7, 19, 20).

Taken together, the present study reports a direct (head-to-head) comparison of the new-generation FIT test and the leading FOB test in 100% biopsy-confirmed colonoscopy-referral setting adequately powered to permit unbiased demonstration of the true differences between the two tests. The ColonView quick test is superior in performance to HemoccultSENSA in detecting fecal occult blood derived from colorectal neoplasia. This difference is most significant for adenomas followed by the combined adenoma/carcinoma endpoint, but disappears for carcinomas. Similarly, the assay testing the Hb/Hp complex is 15% to 8% more sensitive than the detection of Hb-alone, pending on the study endpoints. This difference is most significant in the detection of proximal neoplasia, out of which almost 60% and 50% are missed by HS and the Hb component of CV, respectively, as contrasted to 100% detection by the Hb/Hp complex. These results clearly confirm the recent meta-analytical data on the superiority of FIT test over conventional quaiac-based FOB tests (6, 7, 9, 12-16).

Similarly, the Biohit ColonView quick test is clearly superior to the currently available FIT tests on the market (22-38) shown in a recent meta-analysis by Lee et al. 2014 (21) to exhibit a pooled SE of 79% and pooled SP of 94% for CRC. In the present study, ColonView showed 100% SE and 95.3% SP (AUC=0.977) for proximal colon neoplasia and 98.2% SE and 95.3% SP (AUC=0.968) for the distal neoplasia; both are exceptional performance indicators that advocate the prompt adoption of this new FIT assay as the test-of-choice for CRC screening.