This case-control study, nested within the prospective ATBC Study, provides evidence that serological biomarkers of gastric atrophy are associated with risk of ESCC. PGI levels and the PGI:PGII ratio were both statistically significantly related to ESCC when analyzed as continuous, dichotomous, and ordinal metrics. The full range of analyses and nonlinear modeling of relationships indicated that PGI and PGI:PGII ratio have fairly monotonic relationships with ESCC risk. Thus, gastric atrophy may play a role in the pathogenesis of ESCC, although no association was found with H. pylori, the primary inducer of gastric atrophy.
The first indication of a potential relationship between gastric atrophy and ESCC was provided in 1979 when a case-series of 97 esophageal cancer patients found 63 cases to harbor moderate to marked atrophic gastritis (30
). In 1993, a second study confirmed this observation (31
), and a Swedish cohort study noted a three-fold increased risk of esophageal cancer (88% of which was ESCC) in individuals with pernicious anemia, an ailment associated with severe gastric atrophy (32
Subsequent to these initial observations, six studies (16
) have formally tested the hypothesis that gastric atrophy is associated with ESCC (). As can be seen, all studies which assessed this relationship, whether using serology, histology, or endoscopic appearance for ascertainment of gastric atrophy, found evidence for an association with ESCC which, in totality, provides convincing evidence that the association is real. It remains less clear, however, whether this relationship is causal or results from confounding. If increased severity of gastric atrophy were associated with increased risk of ESCC, this would strengthen the case for the association being causal. Indeed, this is what we found in the current study from the statistical models and graphical representations of the association between PGI, PGI:PGII ratio, and ESCC. Yokoyama et al (20
) also found evidence for a monotonic pattern of association between serum pepsinogens and ESCC in a Japanese population. Further evidence for this pattern has also been provided by a previous study which we conducted in China (26
) in which we demonstrated a monotonic association between PGI:PGII ratio and esophageal squamous dysplasia, which is a known precursor lesion of ESCC (33
). Conversely, there is evidence from serum pepsinogen analyses which do not support a monotonic pattern with ESCC risk (17
) (); although it should be noted that the results from Iijima et al
) ordinal analysis of PGI:PGII (pers. comm.
Dr. K. Iijima, Division of Gastroenterology, Tohoku University Graduate School of Medicine, Japan) are not too dissimilar to the equivalent analysis contained herein, and more extensive scrutiny of the data could prove informative.
Studies which have formally tested the relationship between gastric atrophy, severity of gastric atrophy and ESCC.
also shows that some studies have used other proxy measures to estimate atrophic severity: endoscopy for ascertainment of maximal atrophic extent, and histopathology to ascertain whether an individual harbors intestinal metaplasia or dysplasia. Both of these measures are likely to be inferior relative to serum pepsinogens as proxies of atrophic severity. Endoscopic assessment of atrophic extent is a subjective measurement, and it can be difficult to delineate between atrophic and normal tissues using standard endoscopic visualization (35
). Histologic diagnosis is subject to sampling bias and inconsistent interpretation (36
), both of which may cause misclassification and bias results towards the null. Conversely, serum pepsinogens are an objective measure which provides a global representation of the extent of gastric atrophy.
The Dutch study (18
) reasoned that because ESCC risk did not increase with gastric carcinogenic progression (gastric atrophy to intestinal metaplasia to dysplasia) this was evidence for non-causality. Although degree of intestinal metaplasia, using the Sydney Classification scheme, and the number of gastric biopsies positive for intestinal metaplasia have been correlated with severity of atrophic gastritis (38
), it has not, to our knowledge, been shown that gastric carcinogenic progression (gastric atrophy to intestinal metaplasia to dysplasia) is similarly correlated. In addition, atrophic gastritis is likely to be sufficient for an increased risk of ESCC regardless of intestinal metaplasia and dysplasia status, especially given that the sites of exposure and outcome are distinct.
The Dutch study (18
) does, however, present the most persuasive evidence that the relationship between gastric atrophy and ESCC could be the result of confounding. In addition to their analyses of ESCC, they reported an association between gastric atrophy and small cell lung carcinoma, a relationship which may be difficult to reconcile biologically. In our analyses, adjustment for the major risk factors of ESCC did not change the results, although we cannot rule out the possibility of residual confounding, a problem inherent to all observational epidemiologic studies. Further studies are needed to clarify the issue of causality in the relationship between gastric atrophy and ESCC risk.
We found no association between H. pylori
and ESCC, in agreement with the results of a recent meta-analysis (9
). This lack of association is not necessarily contradictory to our pepsinogen results; there are at least three possible explanations. First, by the age of entry into this study, H. pylori
colonization may have burned itself out, by inducing gastric atrophy and thus destroying the environment in which it thrives, which could result in serologic amnesia (40
). However, we found no difference in the estimates for the association of H. pylori
and ESCC risk when we stratified the analysis by time between blood draw and cancer diagnosis (Supplementary Table 2
); even in those with serum drawn with the shortest time period between blood draw and cancer diagnosis, 20 out of 26 individuals were still H. pylori
seropositive. A second alternative is that ESCC risk could be dependent upon the functional consequences or interactions of H. pylori
, rather than its presence per se
; for example, whether it is able to induce hypochlorhydria (41
) or whether an additional exposure, such as alcohol (42
), increases the likelihood of atrophy, although an analysis stratified by alcohol consumption (Supplementary Table 3
) and a product-term model of our data (p
=0.128) indicated no evidence for multiplicativity. A third alternative is that gastric atrophy/hypochlorhydria could have a different histogenesis in ESCC and may not be primarily dependent upon H. pylori
acquisition. A subset of patients with atrophic gastritis are H. pylori
), and Acinetobacter lwoffii
is known to cause gastric atrophy in mice (45
). However, in the present study, only a single case and no controls were H. pylori
-negative and had a PGI:PGII ratio of less than 4.
Regardless of H. pylori’s
contribution to ESCC carcinogenesis, the evidence indicates that gastric atrophy and hypochlorhydria (41
) are associated with an increased risk of ESCC, but the mechanistic link remains to be elucidated. Bacterial overgrowth and duodenal reflux are possible consequences of atrophy that may play a role. Quantitative and qualitative changes in the microbiota of the gut resulting from hypochlorhydria (46
) could cause increased N-nitrosation reactions, exerting carcinogenic effects on the esophageal mucosa (10
). Duodenal reflux is also known to be carcinogenic (48
), but requires both gastroesophageal and pyloric sphincters to be defective. Distally located ESCC has been associated with severe hypochlorhydria (41
) and gastrectomy (49
), the latter of which vastly increases the propensity for duodenal reflux (51
). Countering this are our exploratory analyses which provided similar estimates of association between gastric atrophy and ESCC across esophageal sites (upper, middle, and lower thirds; Supplementary Table 1
). However, there is also evidence, from animal models (52
) and human epidemiologic studies (56
) that other squamous cell carcinomas of the upper gastrointestinal tract may also be associated with duodenal reflux.
Strengths of our study include the prospective design with long-term follow-up; use of pre-diagnostic serum for analysis of PGI, PGII, and H. pylori antibodies; use of continuous, dichotomous, and ordinal models to interrogate associations; and the availability of covariate information for adjustment of potential confounders. Limitations include modest sample size, a population which includes only male smokers, the possibility of residual confounding, and imperfect correlation between pepsinogen metrics and the true severity of gastric atrophy. Residual confounding could be manifested in the microbiome, which is known to adjust to changes in gastric pH and may also be associated with ESCC risk.
In summary, we have shown that biomarkers of gastric atrophy (PGI and PGI:PGII ratio) are associated with risk of ESCC in the ATBC Cancer Prevention Study. We also find no evidence to suggest that H. pylori, per se, is causal in this relationship. Studies investigating the mechanism relating gastric atrophy and resultant hypochlorhydria to ESCC risk are warranted.