Antibody Responses to Antigens from Helicobacter pylori and Streptococcus gallolyticus Subspecies gallolyticus and Colorectal Cancer–Specific and Overall Survival in the EPIC Cohort

1. Introduction

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers worldwide [1]. Growing evidence suggests that microorganisms, including members of the gut microbiota as well as extraintestinal pathogens, could potentially contribute to CRC development and progression [2]. Microbial dysbiosis and translocation across a compromised intestinal barrier may contribute to chronic inflammation and tumour-promoting processes [3,4]. In this context, antibody responses to bacterial antigens measured in peripheral blood could be used as markers of prior microbial exposure and host–microbe interactions.

Several bacterial species have been implicated in colorectal carcinogenesis, including Helicobacter pylori (H. pylori) [5] and Streptococcus gallolyticus subspecies gallolyticus (SGG) [6]. Although H. pylori primarily colonises the stomach, increasing evidence suggests that infection may also be associated with CRC [5]. A meta-analysis of 47 studies reported that H. pylori infection, ascertained using a range of invasive and non-invasive diagnostic methods was associated with increased CRC risk (odds ratio (OR) = 1.70, 95% confidence interval (CI): 1.64–1.76), although substantial heterogeneity existed between studies [5]. In contrast, prospective studies in Finland [7] and the United States (U.S.) [8] reported null associations for overall H. pylori seropositivity, but growing evidence suggests that responses to specific H. pylori antigens may be more strongly associated with CRC, such as seropositivity to Vacuolating cytotoxin A (VacA) which has been linked to increased CRC risk in European [9] and U.S. populations [10]. Other H. pylori antigens potentially associated with CRC risk include hypothetical proteins HP231, HP305, Neutrophil-activating protein (NapA), Helicobacter cysteine-rich protein C (HcpC), and GroEL [8,9,11]. These antigens include proteins involved in bacterial virulence, immune evasion, oxidative stress defence, and host–pathogen interactions, suggesting multiple mechanisms through which H. pylori may influence colorectal carcinogenesis. Similarly, prospective and patient cohort studies conducted in European and U.S. populations have reported positive CRC risk associations with SGG antibody responses to the pilus proteins Gallo2178 and Gallo2179 [12,13,14]. Together, these findings support a role for host immune responses to microbial antigens as markers of colorectal carcinogenesis.

While most epidemiological studies have focused on CRC incidence, considerably less is known about whether pre-diagnostic host immune responses to microbial antigens are associated with cancer-specific or overall survival after CRC diagnosis.

We therefore evaluated antibody responses to H. pylori and SGG antigens with risk of overall and CRC-specific survival in 471 cases within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. We hypothesized that pre-diagnostic antibody responses to microbial antigens are associated with CRC survival outcomes, reflecting host–microbe interactions relevant to disease progression. Given the increasing incidence of early-onset CRC [15], and emerging evidence linking microbial genotoxins such as Escherichia coli (E. coli) colibactin to early-onset disease [16], we additionally examined associations for the H. pylori and SGG antigens among individuals diagnosed at younger ages (n = 74).

2. Materials and Methods

2.1. Study Population

The EPIC cohort is a large, multicentre cohort study comprising approximately 520,000 participants recruited between 1992 and 2000 from 23 centres across 10 European countries (Denmark, France, Germany, Greece, Italy, The Netherlands, Norway, Spain, Sweden, and the United Kingdom (UK)) [17]. Participants were predominantly aged between 35 and 70 years at enrolment and were drawn mainly from the general population, with some subgroups recruited through breast cancer screening programs (Italy [Florence], The Netherlands [Utrecht]), health insurance systems (France), blood donation services (Spain; Italy [Ragusa, Turin]), and vegetarian or vegan societies (UK [Oxford]).

Blood samples were collected from most participants (>80%) at baseline and processed according to standardized protocols. Samples were stored at the International Agency for Research on Cancer (IARC) in liquid nitrogen at −196 °C [17].

The present analysis involved nested case–control studies within EPIC that have previously investigated antibody responses to H. pylori and SGG in relation to CRC risk [9,12]. Both the studies included participants from 7 of the 10 EPIC European countries (France, Italy, Spain, UK, the Netherlands, Greece, and Germany). Of the 485 incident CRC cases with available multiplex serology data, 471 were included in the current analysis. Participants from Greece (n = 11) were excluded due to data availability restrictions, and additional cases (n = 3 from Spain, the UK, and Germany) were excluded due to invalid matched case-control sets.

The study was approved by the IARC Ethics Committee (Lyon, France) and by the ethics committees at each participating centre. All procedures were conducted in accordance with the Declaration of Helsinki.

2.2. Multiplex Serology for H. pylori and SGG

Antibody responses to 13 H. pylori (strain 26695, except GroEL from strain G27) and 11 SGG proteins (strain UCN34) were measured in pre-diagnostic serum samples using a multiplex serology assay (SeroMap; Luminex Corp., Austin, TX), as previously described [18]. This bead-based fluorescence method allows for the simultaneous detection of immunoglobulin responses (IgG, IgA, and IgM) to multiple bacterial antigens within a single sample.

The level of antibody response is given as median fluorescence intensity (MFI), and cut-off values for antigen-specific seropositivity were defined based on previously established criteria (Table S1, [10,12]), typically derived from the distribution of antibody responses. Overall H. pylori seropositivity was defined as positivity to at least four of the 13 assessed antigens, consistent with the previously validated multiplex serology algorithm demonstrating optimal sensitivity and specificity compared with a commercially available ELISA [19]. To improve specificity, participants were considered positive for an individual H. pylori antigen only if they were also classified as overall H. pylori seropositive. For SGG, seropositivity was determined using a previously validated 6-marker panel (Gallo0272, Gallo0748, Gallo1675, Gallo2018, Gallo2178, and Gallo2179) [13], with individuals classified as positive if they exhibited antibody responses to two or more of these markers. In addition to these definitions, analyses were conducted for individual antigens and for antigen burden categories (1–3, and ≥4 positive antigens compared with 0).

2.3. Cancer and Mortality Ascertainment

Incident CRC cases were identified through linkage with population-based cancer registries or, in certain centres (i.e., France and Germany), through a combination of health insurance databases, pathology registries, and active follow-up procedures [17]. Cases were defined according to the 10th Revision of the International Classification of Diseases (ICD-10) codes. The primary tumours, coded C18–C20, were considered CRC cases (n = 471), early-stage CRC consisted of stage I and II cancers (n = 153) and advanced stage CRC consisted of stage III to IV cancers (n = 165). Information on age at diagnosis, tumour location (colon or rectum), and tumour stage was obtained from medical and registry records. CRC diagnoses included in this analysis occurred between 1993 and 2003. Completeness of tumour stage data varied across centres, with some centres providing complete information and others having partial or missing data.

Information on vital status was obtained using a combination of active follow-up and linkage to national or regional mortality registries, depending on the country [17,20]. In France and Germany, follow-up involved direct contact with participants or next-of-kin, as well as linkage to health insurance and pathology records, whereas in other countries (Italy, Spain, The Netherlands, and the UK), mortality data were obtained through regional and/or national mortality registry linkage. In Naples (Italy), cancer incidence was ascertained through active follow-up.

Causes of death were coded according to ICD-10 classification. Follow-up time was defined from the date of CRC diagnosis until death or the last known date of follow-up, whichever occurred first. End of follow-up varied across centres, typically ranging between 2009 and 2014.

2.4. Measurement of Covariates

At baseline, participants provided detailed information on demographic, lifestyle, and behavioral factors via standardized questionnaires. Variables collected included age, sex, educational attainment, smoking status, physical activity and dietary intake including alcohol consumption, red and processed meat, and dietary fibre intake [17].

Anthropometric measurements, including weight and height, were obtained by trained personnel using standardized procedures, except in certain centres (France and UK [Oxford]) where self-reported measurements were used. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared (kg/m²).

2.5. Statistical Analysis

Person-time was calculated from the date of CRC diagnosis to death or censoring at the end of follow-up. Associations between antibody responses and mortality outcomes were calculated using multivariable Cox proportional hazards regression models with time since CRC diagnosis used as underlying time scale. Hazard ratios (HRs) and 95% CIs were estimated for CRC-specific mortality (HR_CRC) and all-cause mortality (HR_ACM; HR for overall mortality). All models were stratified by the country of diagnosis. Two multivariable adjustment models were evaluated. Model 1 was adjusted for body mass index (BMI; continuous), highest educational attainment (none, primary school, technical/professional school, secondary school, and university), smoking status (never, former, current, or unknown), and alcohol intake (g/day; continuous), consistent with the adjustment strategy used in the original CRC risk assessment analysis [9,12]. Model 2 was additionally adjusted for potential confounders, including age at diagnosis (continuous), sex (male or female), combined total physical activity index modelled according to the Cambridge physical activity categories (inactive, moderately inactive, moderately active, and active) and tumour site (colon or rectum). Two sensitivity analyses were conducted. First, a two-year delayed-entry analysis was performed, in which participants entered the risk set two years after diagnosis and those with follow-up of two years or less were excluded, to assess whether the observed associations were driven by early deaths after diagnosis. The second analysis was restricted to individuals who provided blood samples within two years before CRC diagnosis evaluating if associations were similar when antibody measurements were obtained close to diagnosis.

Potential differences in associations by sex were assessed by fitting Cox proportional hazards models containing interaction terms between sex and each serological exposure. Sex-specific HR and 95% CIs were estimated from the interaction models, and heterogeneity between males and females was evaluated using likelihood-ratio tests comparing models with and without the interaction term. An exploratory subgroup analysis was conducted among participants diagnosed < 55 years of age. This age threshold was selected because of the limited number of younger CRC cases and is consistent with a previous analysis conducted within the EPIC cohort [21]. To account for potential dietary confounding, a sensitivity analysis was performed with Model 2 additionally adjusted for red and processed meat intake and dietary fibre intake (g/day; continuous). Joint associations between H. pylori and SGG seropositivity and mortality outcomes were also evaluated. Multiplicative interactions between H. pylori and SGG seropositivity were assessed by including an interaction term in the Cox models. Interaction analyses were conducted to assess whether the associations between H. pylori or SGG seropositivity and CRC survival differed according to seropositivity for the other bacterium. Additional analyses examined associations of high H. pylori (≥4 antigens) and high SGG (≥2 antigens) antigen burden, individually and jointly, with mortality outcomes. All statistical analyses were performed using R (version 4.3.1), and all tests were two-sided with a statistical significance level of p ≤ 0.05. To account for multiple testing, Benjamini - Hochberg false discovery rate (FDR) correction was applied to the analyses.

3. Results

A total of 471 incident CRC cases were included in the analysis, among whom 254 all-cause deaths and 188 CRC-specific deaths occurred during a median follow- up of 9.2 years (IQR: 1.8 – 15.3 years). CRC diagnoses occurred between 0.4 and 8.5 years following blood collection, with a median interval of 3.4 years. Baseline characteristics were broadly similar across categories of antibody response, with no consistent patterns observed for lifestyle factors (Table 1). Seroprevalence varied across individual antigens for both H. pylori and SGG (Table 2), ranging from 9.8% (HpaA) to 46.9% (GroEL) for H. pylori antigens and from 5.5% (Gallo0112b) to 14.9% (Gallo0748) for SGG antigens.

Overall seropositivity to H. pylori or SGG antigens was not associated with CRC-specific or overall mortality (Table 2). Similarly, no associations were observed according to antigen burden (“1–3”, “≥4” positive antigens compared with none). However, among patients with advanced-stage CRC, overall H. pylori seropositivity was associated with lower CRC-specific mortality (HR_CRC = 0.55, 95% CI: 0.33–0.93, p = 0.03, Table S2) in multivariable model 1. No associations were observed in the two-year delayed-entry sensitivity analysis (Table S3). Among participants whose blood was collected <2 years prior to cancer diagnosis, seropositivity to ≥4 H. pylori antigens was associated with lower CRC-specific mortality (HR_CRC = 0.22, 95% CI: 0.07–0.72, p = 0.01, Table S4) and all-cause mortality (HR_ACM = 0.23, 95% CI: 0.07–0.69, p = 0.01, Table S4). Following additional adjustment for dietary factors, the inverse association between overall H. pylori seropositivity and CRC-specific mortality among patients with advanced-stage CRC was retained (HR_CRC = 0.54, 95% CI: 0.29–1.01, p = 0.05, Table S5).

At the individual antigen level, seropositivity to H. pylori catalase was associated with lower CRC-specific mortality in model 1 (HR_CRC = 0.71, 95% CI: 0.49–1.01, p = 0.05, Table 2). This inverse association was also observed among patients with advanced-stage disease in both model 1 (HR_CRC = 0.55, 95% CI: 0.33–0.93, p = 0.03, Table S2) and model 2 (HR_CRC = 0.38, 95% CI: 0.19–0.77, p = 0.01, Table S6). In analyses restricted to cases with blood samples collected within 2 years prior to diagnosis, catalase seropositivity was associated with reduced CRC-specific mortality (HR_CRC = 0.16, 95% CI: 0.04–0.55, p = 0.004, Table S4) and all-cause mortality (HR_ACM = 0.22, 95% CI: 0.08–0.63, p = 0.005, Table S4). In the analysis with additional adjustments for dietary factors, an inverse association for catalase with CRC-specific mortality in advanced stage CRC was observed (HR_CRC = 0.43, 95% CI: 0.21–0.86, p = 0.02, Table S5).

Other individual H. pylori antigens were also associated with CRC-specific mortality in patients with early-stage disease. In model 1, seropositivity to HpaA was associated with an increased risk of CRC-specific mortality (HR_CRC = 3.91, 95% CI: 1.34–11.38, p = 0.01, Table S2). In model 2, seropositivity to HcpC (HR_CRC = 6.85, 95% CI: 1.17–40.01, p = 0.03, Table S6), HP0305 (HR_CRC = 7.56, 95% CI: 1.10–51.85, p = 0.04, Table S6), and HpaA (HR_CRC = 19.89, 95% CI: 3.07–128.72, p = 0.002, Table S6) were associated with increased CRC-specific mortality. However, these estimates should be interpreted cautiously because of the wide CIs, reflecting the limited number of events in this subgroup.

For SGG, most individual antigens were not associated with mortality outcomes (Table 2). However, seropositivity to Gallo1570 was associated with lower all-cause mortality in model 2 (HR_ACM = 0.57, 95% CI: 0.35–0.93, p = 0.03; Table 2). In the early-stage subgroup, seropositivity to Gallo0748 was associated with increased CRC-specific mortality in model 1 (HR_CRC = 4.07, 95% CI: 0.98–16.86, p = 0.05, Table S2).

In the analysis excluding the first 2 years of follow-up after CRC diagnosis, H. pylori antigen HP0305 was associated with increased risk of CRC-specific mortality (HR_CRC = 1.88, 95% CI: 1.02–3.47, p = 0.04, Table S3). Among SGG antigens, SGG seropositivity category (≥4 vs. 0 antigens) was associated with higher all-cause mortality (HR_ACM = 2.25, 95% CI: 0.99–5.10, p = 0.05, Table S3) and Gallo0112a was associated with an increased risk of CRC-specific mortality (HR_CRC = 2.78, 95% CI: 1.21–6.37, p = 0.02, Table S3).

In the analysis conducted on individuals with blood drawn <2 years prior to CRC diagnosis, H. pylori proteins GroEL, Urea, and VacA were associated with lower risks of both CRC-specific and all-cause mortality (GroEL: HR_CRC = 0.15, 95% CI: 0.04–0.52, p = 0.003 and HR_ACM = 0.12, 95% CI: 0.04–0.39, p <0.001; Urea: HR_CRC = 0.25, 95% CI: 0.08–0.76, p = 0.01 and HR_ACM = 0.23, 95% CI: 0.08–0.66, p = 0.01; VacA: HR_CRC = 0.16, 95% CI: 0.04–0.65, p = 0.01 and HR_ACM = 0.13, 95% CI: 0.04–0.43, p < 0.001). NapA was associated with lower all-cause mortality (HR_ACM = 0.28, 95% CI: 0.08–1.01, p = 0.05). Among SGG antigens, Gallo2018 was associated with an increased risk of all-cause mortality (HR_ACM = 4.42, 95% CI: 1.23–15.94, p = 0.02), whereas Gallo2178 was associated with a lower risk of all-cause mortality (HR_ACM = 0.19, 95% CI: 0.05–0.74, p = 0.02) (Table S4).

Among early-onset CRC cases, inverse associations with CRC-specific mortality were observed for H. pylori CagA (HR_CRC = 0.04, 95% CI: 0.00–0.86, p = 0.04, Table S7). No significant associations were observed for SGG antigens in early-onset CRC cases.

In sex-stratified analyses, associations were similar in males and females. However, evidence of interaction by sex was observed for H. pylori HpaA in all-cause mortality (interaction p = 0.05) and for SGG Gallo2178 in CRC-specific mortality (interaction p = 0.05). Among males, HP0231 was associated with lower CRC-specific mortality (HR_CRC = 0.56, 95% CI: 0.33–0.97, p = 0.04). Seropositivity to Gallo2178 was inversely associated with both CRC-specific mortality (HR_CRC = 0.40, 95% CI: 0.17–0.92, p = 0.03) and all-cause mortality (HR_ACM = 0.42, 95% CI: 0.20–0.89, p = 0.02) in female. In addition, Gallo1570 was inversely associated with all-cause mortality among females (HR_ACM = 0.42, 95% CI: 0.23–0.79, p = 0.01) (Table 3).

No evidence of interaction between H. pylori and SGG seropositivity was observed for all-cause mortality, CRC-specific mortality, or CRC-specific mortality among advanced-stage cases (all interaction p-values > 0.05; Table S8). Similarly, analyses examining the joint effects of high H. pylori (≥4 antigens) and high SGG (≥2 antigens) antigen burden showed no significant associations with mortality outcomes (Table S9).

4. Discussion

In this study, we evaluated pre-diagnostic antibody responses to H. pylori and SGG in relation to CRC survival within the EPIC cohort. Using multiplex serology, we assessed systemic immune responses to a panel of bacterial antigens and examined their association with both overall and CRC-specific mortality. While overall seropositivity to H. pylori and SGG, including the CRC-specific SGG 6-marker panel, was not associated with survival outcomes, seropositivity to specific bacterial antigens for either H. pylori or SGG was associated with CRC prognosis. This includes H. pylori catalase, associated with lower CRC-specific mortality, whereas SGG Gallo1570 was inversely associated with all-cause mortality.

Previous studies have consistently linked antibody responses to H. pylori and SGG with colorectal neoplasia. This includes case-control studies within our group where we found IgG seropositivity to the H. pylori antigen HpaA and IgA seropositivity to SGG proteins (Gallo0272 and Gallo1675) to be associated with an increased risk of advanced adenomas, suggesting a role for these bacteria across different stages of disease development [20,21]. In prospective studies, including analyses within the EPIC cohort and in U.S. populations, seropositivity to H. pylori antigens HcpC and VacA, as well as positivity to ≥2 SGG proteins within a predefined 6-marker panel, were associated with an increased risk of CRC development in pre-diagnostic serum samples [9,10,12].

Although the underlying mechanisms remain uncertain, the sensitivity analysis restricted to participants whose blood was collected less than two years before CRC diagnosis yielded similar or stronger associations for several individual antigens, suggesting that the findings were not influenced by developing tumours. Nevertheless, the observational nature of this study precludes conclusions regarding causality or the biological mechanisms underlying these associations. One possibility for our findings is that systemic antibody responses represent markers of effective immune control, whereby prior exposure contributes to enhanced immune surveillance and improved prognosis. Alternatively, these responses may reflect persistent or dysregulated host–microbial interactions associated with tumour progression. In this context, microbial translocation across a compromised intestinal barrier and subsequent immune activation may play a role, as previously proposed for other gut-associated bacteria, including genotoxic E. coli and enterotoxigenic Bacteroides fragilis (ETBF) [24]. This interpretation is consistent with the “driver–passenger” model of microbial involvement in CRC, whereby certain bacteria may contribute to tumour initiation [25], while other opportunistic bacteria preferentially colonize the tumour microenvironment as a consequence of disease progression. In this framework, H. pylori and SGG may be more relevant during early stages of carcinogenesis [20,21], whereas their role in established tumours and survival outcomes may be indirect.

In the current study, seropositivity to H. pylori catalase was associated with lower CRC-specific mortality. Similar inverse associations were observed among participants with advanced-stage CRC in both the fully adjusted multivariable model and the model with additional adjustment for dietary factors, suggesting that the association was robust across different analytical approaches. Catalase (KatA) is a major antioxidant enzyme that protects H. pylori from host-derived reactive oxygen species (ROS), facilitating bacterial survival and persistence during infection [24,25]. Beyond its antioxidant function, catalase acts as a moonlighting protein with multiple virulence-related activities, including binding to host glycoprotein vitronectin, inhibiting membrane attack complex recognition, and thereby promoting immune evasion [28]. Catalase has also been implicated in cholesterol binding and uptake, mechanisms that may further contribute to bacterial persistence within the host [29].

Experimental studies have demonstrated that catalase is essential for H. pylori survival under oxidative stress [27] and can protect transformed epithelial cells from ROS-mediated apoptosis [30]. Despite these virulence-associated properties, the observed inverse association between catalase seropositivity and CRC-specific mortality likely reflects host immune responses rather than a direct protective effect of the bacterial protein itself. Notably, H. pylori catalase possesses unique structural (tetra-lysine motif) and antigenic features, and antibodies directed against KatA show limited cross-reactivity with mammalian catalases, supporting it as a marker of host recognition of H. pylori infection [29,30].

One possible explanation for our findings is that catalase seropositivity reflects a more effective host immune response. Previous studies have shown that recognition of H. pylori epitopes can elicit a predominantly Th1/IFN-γ-mediated immune response, accompanied by reduced Th2/IL-4 activity, which has been associated with more effective control of H. pylori infection [33]. In this context, anti-catalase antibodies may represent a marker of prior immune control or clearance of infection, or more broadly, a host immune phenotype associated with improved tumour surveillance and survival. Our findings therefore highlight the distinction between the biological functions of bacterial virulence factors and the prognostic significance of host antibody responses directed against them.

We further observed heterogeneity by sex. Among H. pylori antigens, HpaA demonstrated evidence of interaction by sex and HP0231 was associated with lower CRC-specific mortality in males. In the younger-onset subgroup, an inverse association with CRC-specific mortality was observed for CagA. These findings may suggest sex- and age-related differences in immune responses or host–microbial interactions, although they should be interpreted cautiously given limited subgroup sizes. The contrasting associations observed by sex may reflect differences in immune function, as women generally exhibit stronger innate and humoral immune responses than men, or it could be attributable to a different microbiome composition [34,35,36]. In addition, age-related changes in the gut microbiome, particularly during age 40 and 60 may also contribute to the age-specific associations observed in our study [37]. Although H. pylori infection prevalence is typically higher among men, this reflects exposure rather than host immune response [38]. Previous serological studies have not consistently reported sex-specific differences in antibody responses to individual H. pylori antigens, including CagA, VacA, and catalase [39]. The heterogeneity observed in our study may therefore reflect differences in disease context or host–tumour interactions rather than baseline infection patterns.

For SGG, we found limited evidence of associations with survival despite its proposed role in colorectal carcinogenesis. Previous studies, including a Spanish case–control study [40] and the prospective EPIC study [12], reported associations between CRC and the pilus protein Gallo2178, a putative virulence factor [38,39]. In our sex stratified analysis, we found that Gallo2178 and Gallo1570 (another pilus protein) demonstrated inverse associations with all-cause mortality in females. Gallo2178 was also associated with lower CRC-specific mortality among females.

Strengths of this study include its prospective design, use of pre-diagnostic samples, standardized multiplex serology, and long-term follow-up up within a large, multicentre cohort. However, certain limitations should be considered. The small sample size of the CRC cases was a major limitation and could have contributed to the lack of statistical power. Although multiple-testing correction was performed, the associations did not remain statistically significant following FDR adjustment. However, such correction may be overly conservative in the present study because the analyses were hypothesis-driven, based on a targeted panel of biologically relevant antigens selected a priori from previous evidence [10,13] rather than an exploratory analysis. Further, the EPIC cohort predominantly comprises individuals of European ancestry, and replication in larger and more diverse populations, including those with differing H. pylori and SGG epidemiology, could improve generalisability of our findings. Furthermore, antibody responses represent indirect measures of exposure and do not capture the presence or activity of bacteria within the tumour microenvironment. As the current study is observational in nature, residual confounding and reverse causation cannot be completely excluded, despite our prospective design and sensitivity analyses.

5. Conclusions

There were limited associations observed between overall seropositivity to H. pylori and SGG and CRC survival outcomes. However, the observed associations at the level of specific bacterial antigens, particularly the inverse association between H. pylori catalase seropositivity and CRC-specific mortality, suggest that antigen-specific host immune responses may be more informative for CRC prognosis than overall seropositivity. These findings indicate that while overall microbial exposure may not influence disease progression, antigen-specific antibody responses could reflect underlying host–microbe interactions or immune profiles associated with survival outcomes. Further studies with larger sample sizes and independent cohorts are required to validate these findings and to determine whether serological responses to microbial antigens may serve as potential biomarkers of prognosis or reflect broader immune mechanisms relevant to CRC survival.