The fecal immunochemical test works by detecting hemoglobin, the oxygen-carrying protein of red blood cells, that has leaked into the digestive tract from precancerous growths or tumors. Unlike the older guaiac-based stool tests, FIT does not react with hemoglobin from food, so it can be calibrated to a precise concentration, typically expressed in micrograms of hemoglobin per gram of feces. Lowering the threshold makes the test more sensitive, catching more cancers and precancerous lesions, but it also floods screening programs with false positives, each of which triggers an expensive and invasive colonoscopy. Raising the threshold does the opposite, sparing colonoscopy capacity but missing more early disease. For countries like China, where screening is being rolled out across enormous populations with limited endoscopy resources, that trade-off is not an academic curiosity; it determines whether a program is feasible at all.

To pin down the optimal balance, a team led by Yanxiu Liu and Nan Zhang of Shandong Cancer Hospital and Institute, together with collaborators at Shandong University and other provincial institutions, recruited asymptomatic residents aged 40 to 74 across 13 regions of Shandong Province. All participants were considered average risk, meaning they had no personal or family history suggesting elevated colorectal cancer risk and no symptoms that would already warrant diagnostic investigation. Each volunteer provided a stool sample for FIT analysis and then underwent a full colonoscopy, the gold standard against which the test’s performance could be measured. The researchers tracked three outcomes: colorectal cancer itself, advanced adenomas, which are precancerous polyps with a high potential to turn malignant, and the combined category of advanced colorectal neoplasia, which encompasses both.

The final analysis included 5,918 participants, a cohort in which 378 people, or 6.4 percent, turned out to have advanced adenomas and 28 people, or 0.5 percent, had colorectal cancers. Those numbers illustrate why screening matters: advanced adenomas were more than thirteen times as common as outright cancers, and detecting them early offers the chance to prevent malignancy rather than merely treat it. When the researchers evaluated FIT performance at a threshold of 25 micrograms of hemoglobin per gram of feces, the test detected 96.4 percent of the cancers found at colonoscopy, with a 95 percent confidence interval stretching from 89.3 to 100 percent. Sensitivity for advanced adenomas was considerably lower, at 40.2 percent, and for advanced colorectal neoplasia overall it was 44.1 percent, reflecting the well-known limitation that many precancerous polyps shed too little blood to trip even a low FIT cutoff.

Specificity, the proportion of people without disease who correctly test negative, remained impressively high at the same threshold: 95.6 percent for advanced adenoma, 93.8 percent for cancer, and 96.1 percent for advanced colorectal neoplasia. In practical terms, fewer than one in twenty average-risk residents without neoplasia would be falsely flagged at the 25 microgram cutoff. The researchers also calculated a measure called the number needed to scope, which quantifies the screening burden by counting how many colonoscopies must be performed to find one lesion. If everyone in the population went straight to colonoscopy without any preliminary stool testing, the program would need 211.4 colonoscopies to detect a single cancer and 14.6 to detect one case of advanced colorectal neoplasia. Using FIT at the 25 microgram threshold as a filter, those figures collapsed to 14.6 colonoscopies per cancer and just 2.2 per advanced neoplasia, a reduction of roughly ninety-three percent in the endoscopy burden per cancer detected.

That arithmetic is the heart of the study’s argument. FIT does not outperform colonoscopy in raw detection, but it transforms the economics of screening by concentrating endoscopy resources on the small fraction of people most likely to harbor disease. At a threshold of 25 micrograms per gram, the test misses some advanced adenomas, yet it still identifies the overwhelming majority of cancers while eliminating more than nine out of ten unnecessary colonoscopies. For a screening program, that means a fixed endoscopy budget can cover a vastly larger population, and the study’s authors argue that this balance between detection and resource use is what threshold selection is really about.

The Shandong team then took the analysis a step further by dividing the 13 regions into two groups according to their baseline colorectal cancer incidence, comparing relatively high-incidence areas with relatively low-incidence ones. The subgroup results point toward a strategy that has rarely been articulated so concretely: in regions where colorectal cancer is relatively common, the 25 microgram threshold appeared to provide a more favorable balance between detection and colonoscopy burden, because the higher sensitivity pays off when the underlying prevalence of disease is greater. In regions where the disease is relatively rare, a higher threshold of 50 micrograms per gram mainly improved specificity and screening efficiency, since lowering the cutoff in a low-prevalence population would generate a cascade of false positives that overwhelms endoscopy capacity without proportionally more cancers found.

This prevalence-dependent logic follows directly from the mathematics of predictive values. The positive predictive value of any test rises with disease prevalence, so the same FIT result carries more weight in a high-incidence region than in a low-incidence one. Conversely, when prevalence falls, the cost of each false positive grows relative to the benefit of each true positive, and a stricter threshold conserves resources. The Shandong data suggest that a one-size-fits-all national cutoff may leave efficiency on the table, and that region-specific calibration, informed by local cancer registries, could squeeze more screening value out of the same budget. The authors are careful to note, however, that these subgroup findings require further validation before region-specific strategies can be formally recommended, since the regional division was based on baseline incidence and the cohort, while large, was not designed to test regional strategies head-to-head.

The study arrives at a moment when colorectal cancer screening is expanding across China and other middle-income countries, and when health systems everywhere are grappling with the question of how to screen aging populations without exhausting endoscopy capacity. FIT is already the backbone of organized screening programs in many parts of the world, precisely because it is cheap, noninvasive, and can be administered by mail. But the new results underscore that the test’s value is not fixed; it is a dial that program designers must set according to local disease burden, endoscopy availability, and the goals of the program. A threshold that works well in a high-incidence province may squander resources in a low-incidence one, and the Shandong evidence provides a quantitative anchor for those decisions.

For average-risk residents, the practical takeaway is straightforward: a stool test at a carefully chosen cutoff can identify the great majority of colorectal cancers while sparing more than nine out of ten people an unnecessary colonoscopy, and the cutoff that achieves this balance may depend on where they live. The researchers conclude that a threshold of 25 micrograms of hemoglobin per gram appeared to provide a favorable overall balance in this average-risk population, while their further analyses suggest that optimization may vary across regions with different colorectal cancer incidence. As screening programs scale up, the study offers a template for evidence-based threshold selection, one that could help health systems detect more cancers with the endoscopies they already have, and it adds a compelling data point to the growing science of precision public health, where even a number printed on a stool test kit can shape who lives and who dies.

Subject of Research: Cancer Screening

Article Title: Optimizing thresholds of fecal immunochemical test for colorectal cancer screening in average-risk residents

Article References: Liu, Y., Feng, Y., Gao, Q., Ji, J., Lu, C., Zhang, X., Ma, H., Sun, X., & Zhang, N. (2026). Optimizing thresholds of fecal immunochemical test for colorectal cancer screening in average-risk residents. BMC Cancer. https://doi.org/10.1186/s12885-026-16967-3

Image Credits: AI Generated

DOI: 10.1186/s12885-026-16967-3

Keywords: colorectal cancer, fecal immunochemical test, FIT threshold, colonoscopy, cancer screening, advanced adenoma, screening burden, Shandong Province, BMC Cancer, precision public health, Optimizing, thresholds

The research team enrolled participants in six distinct groups to capture the progression spectrum. These included a low-risk group of individuals under 45 years of age with no intestinal lesions detected by colonoscopy, a high-risk group of individuals aged 45 or older who likewise showed no lesions, patients with advanced adenomas, and patients with colorectal cancer at stages I and II, stage III, and stage IV. This staged design allowed the investigators to ask a question that has long fascinated microbiome researchers: do the microbial signatures of colorectal cancer emerge abruptly, or do they shift gradually and measurably as the disease moves from precancerous lesions to invasive and metastatic stages?

The metagenomic results were striking in their directional consistency. Several dominant bacterial genera showed progressively lower relative abundance as cancer stage advanced. These declining taxa included UBA7182, Lachnoclostridium B., Faecalibacillus, Fusicatenibacter, and Anaerobutyricum—genera that are broadly associated with a healthy, fermentative gut environment and the production of beneficial short-chain fatty acids. Their steady erosion across stage groups suggests that the metabolic functions these organisms perform, such as butyrate production that nourishes colonocytes and supports anti-inflammatory signaling, may gradually diminish as the tumor microenvironment evolves. Conversely, two genera moved in the opposite direction: Intestinimonas and Bacteroides showed higher relative abundance in more advanced disease groups, hinting at a compositional takeover in which opportunistic or stress-tolerant organisms replace the beneficial core community.

Perhaps the most consequential transition occurred between the high-risk group and the advanced adenoma group. At the boundary between healthy tissue and early neoplastic transformation, the researchers observed a marked decline in the detection rate of low-abundance taxa at the sequencing depth used in the study, together with a measurable reduction in overall microbial diversity. In ecological terms, the arrival of advanced adenomas appears to coincide with a simplification of the gut bacterial ecosystem—a loss of rare species that may function as sensitive early-warning indicators. If confirmed in prospective cohorts, this diversity collapse could become a focal point for the development of early-detection strategies, since a dwindling rare biosphere may register in stool-based assays before symptoms ever appear.

The metabolomic arm of the study added a layer of biochemical context, though with an important interpretive caveat. When the researchers compared the low-risk and high-risk groups—defined strictly by age at 45 years—they found metabolomic differences that appeared to be driven largely by age and age-associated factors rather than by early-disease biology. This distinction matters because it guards against overinterpreting metabolic shifts between the two healthy comparison groups as evidence of preclinical cancer. Within the disease-related analyses, putatively annotated metabolite features, classified at confidence Levels 2 and 3 of the Metabolomics Standards Initiative, mapped onto eight candidate KEGG pathway modules, pointing to perturbed biochemical routes that accompany malignant progression, including pathways connected to energy metabolism and the pentose phosphate pathway, a route with established roles in rapid cell proliferation.

The ionomic analysis, a less common but technically demanding component of multi-omics studies, profiled elemental concentrations in the samples and revealed stage-specific signatures of essential and trace elements. Strontium, iron, and phosphorus reached their highest levels in stage III colorectal cancer, a stage characterized by lymph node involvement and often intensive systemic change. Beryllium predominated in the low-risk individuals, while sulfur was enriched in both the low-risk and high-risk groups. Although the biological significance of these elemental patterns remains to be fully worked out, ions such as iron are known to influence both host physiology and bacterial competition in the gut, and the study’s findings suggest that ionic profiles shift in tandem with microbial and metabolic changes as the disease progresses.

To synthesize these three data layers—microbial taxa, metabolites, and elemental profiles—the researchers applied integrated analytical frameworks, including multi-omics factor analysis and machine learning classifiers such as support vector machines, alongside conventional ordination techniques like principal component analysis and Bray-Curtis dissimilarity measures. The integrated evidence converged on a central conclusion: microbiota, metabolites, and ionic profiles differ across colorectal cancer stage groups, including the earliest disease-stage groups. This convergence across independent molecular domains strengthens the case that the gut microbiome ecosystem is not a passive bystander in colorectal cancer but a dynamic system whose architecture is reshaped in step with tumor progression.

The authors are careful to frame their findings as hypothesis-generating rather than diagnostic. Because the study was cross-sectional, with no within-individual longitudinal sampling, it cannot directly observe progression within a single patient; the stage-associated differences describe correlations between groups, not causal trajectories in individuals. The researchers also flag two specific limitations that warrant particular caution against over-interpretation. First, the low-risk and high-risk groups differ by age—younger than 45 versus 45 and older—so differences between them are confounded by age and cannot be fully statistically adjusted. Second, no microbiome positive or negative controls, such as mock communities, extraction blanks, or no-template controls, were included, meaning reagent and background contamination cannot be fully excluded and the low-abundance findings must be treated as exploratory. Before any diagnostic application, the patterns described here would need to be validated in independent prospective cohorts.

Even with these caveats, the scale and breadth of the study mark a significant advance in cancer microbiome research. Colorectal cancer remains one of the most common and deadly malignancies worldwide, and growing evidence links its etiology to complex interactions among gut microbiota alterations, metabolic dysregulation, and disturbances in essential ions. By simultaneously mapping all three dimensions across a staged cohort of nearly a thousand samples, the work provides a resource for researchers seeking microbial or metabolic biomarkers of disease stage, and it sharpens the scientific conversation about how aging, microbial ecology, and tumorigenesis intertwine. The observed interplay between the microbiome and senescence—the biological aging process—emerges as a particularly promising frontier, and the authors position their correlation-level findings as a foundation for future longitudinal studies that could ultimately translate these ecosystem-level signatures into tools for earlier detection and better risk stratification of colorectal cancer.

Subject of Research: Stage-associated changes in the gut microbiome ecosystem across colorectal cancer progression

Article Title: Multi-omics analysis reveals stage-associated differences in the gut microbiome ecosystem across stages of colorectal cancer in a cross-sectional cohort

Article References: Shuwen, H., Jian, C., Yinhang, W., Yating, X., Caiyun, C., Zefeng, W., Shuwen, L., Peng, Q., Xi, Y., & Wei, W. (2026). Multi-omics analysis reveals stage-associated differences in the gut microbiome ecosystem across stages of colorectal cancer in a cross-sectional cohort. BMC Medicine. https://doi.org/10.1186/s12916-026-05218-8

Image Credits: AI Generated

DOI: 10.1186/s12916-026-05218-8

Keywords: colorectal cancer, gut microbiome, metagenomics, metabolomics, ionomics, microbial diversity, advanced adenoma, cancer staging, BMC Medicine, multi-omics, gut microbiota, biomarkers