Urinary estrogen metabolites and gastric cancer risk among postmenopausal women

Abstract Background The overall incidence of gastric cancer in women is half that in men for most global populations. Sex hormone pathways may be involved in carcinogenesis and estrogens have been postulated to protect women against gastric cancer. Aim To evaluate associations of gastric cancer with estrogen metabolites in postmenopausal women. Methods and results We performed an analysis of 233 gastric cancer cases and 281 age‐matched controls from three prospective cohorts and two case‐control studies of early‐stage gastric cancer, mainly conducted in high‐risk Asian populations. Fifteen estrogen‐parent (estrone and estradiol) and ‐metabolite analytes (2‐hydroxyestrone, 2‐hydroxyestradiol, 2‐hydroxyestrone‐3‐methyl ether, 4‐hydroxyestrone; 4‐methoxyestrone, 4‐methoxyestradiol, 2‐methoxyestrone, 2‐methoxyestradiol, estriol, 16α‐hydroxyestrone, 16‐ketoestradiol, 16‐epiestriol, and 17‐epiestriol) were measured in spot urines using liquid chromatography–tandem mass spectrometry. Odds ratios for association with each marker were estimated by logistic regression. Heterogeneity was assessed by Cochran's Q test. Study‐specific odds ratios were pooled by fixed‐effects meta‐analysis. Urinary levels of estrogen‐related molecules were not associated with gastric cancer (adjusted odds ratios ranged from 0.87 to 1.27; p‐values >.05), with low between‐study heterogeneity (p‐values >.1) for all but two metabolites (2‐hydroxyestrone‐3‐methyl ether and 2‐methoxyestradiol). Conclusion To date, this is the first comprehensive assessment of endogenous estrogens with gastric cancer risk in women. Estrogens do not appear to have an etiologic role in gastric cancer risk among postmenopausal women. Given the complex network of sex steroid hormones and their extreme variation over the lifespan, further evaluation of this hypothesis is warranted.

Conclusion: To date, this is the first comprehensive assessment of endogenous estrogens with gastric cancer risk in women. Estrogens do not appear to have an etiologic role in gastric cancer risk among postmenopausal women. Given the complex network of sex steroid hormones and their extreme variation over the lifespan, further evaluation of this hypothesis is warranted.

| Study population
Our analysis included 216 women from three population-based prospective studies (Korean Multicenter Cancer Cohort, 5 Iranian Golestan Cohort, 6 and German ESTHER Cohort 7 ) and 298 women from two case-control studies of early-stage cancer (American Joint Committee on Cancer clinical stages 1A or 1B) from Japan 8 and Korea. Gastric cancer cases were identified based on the International Classification of Diseases (10th Revision), codes C16. In total, 233 postmenopausal women (with known postmenopausal status or age 60 years or older) with gastric cancer (85% non-cardia tumors) were frequency-matched by study and 5-year age category to 281 gastric cancer-free controls. For the prospective samples, the median time from urine collection to cancer diagnosis ranged from 5 (Golestan cohort) to 7.4 (ESTHER cohort) years. This analysis was restricted to women not taking exogenous hormones and included all available gastric cancer cases (at least five per study) at the time of selection. Spot urine specimens were collected at enrollment in prospective studies and pre-treatment in case-control studies.

| Statistical analysis
We calculated pairwise Spearman's rank correlation coefficients among urinary metabolites using the controls. We used logistic regression to evaluate the association between the risk of gastric cancer and the log 2 concentration of each metabolite. We report the study-specific odds ratios (OR) and 95% confidence intervals from models that stratify by batch and adjust for age (continuous), body mass index (continuous) and, when available, smoking (ever vs. never), alcohol use (ever vs. never), education (none vs. any) and family history of gastric cancer (yes vs. no).
This information was collected at enrollment in prospective studies and pre-treatment in case-control studies. Study-specific ORs were averaged via fixed-effects meta-analysis using the "metafor" R package, with heterogeneity assessed by Cochran's Q test. A p-value less than .05 was considered statistically significant, except for test of heterogeneity for which we used a p-value cut-off of .1. Given the exploratory nature of our study, results were not corrected for multiple comparisons.

| RESULTS
Baseline characteristics of gastric cancer cases and controls are presented in Table 1. Most cases represented noncardia gastric cancer.

| DISCUSSION
The reasons for sex differences in gastric cancer are not well elucidated.
Despite the plausible biologic evidence from epidemiologic, 3 laboratory and clinical studies, 9,10 our multicenter study found that urinary concentrations of parent estrogens and their metabolites in postmenopausal women were not associated with gastric cancer risk. We found a similar null association with estradiol in a case-control study of invasive noncardia gastric cancer using diagnostic blood samples. 11 This study is the first epidemiologic analysis that directly evaluated estrogen metabolism in gastric carcinogenesis in women using samples collected prior to cancer diagnosis or asymptomatic localized disease (with limited opportunity for reverse causality). We also used a sensitive and specific mass spectrometry method to accurately quantitate estrogens. Our study is informative as it mainly included women from high gastric cancer risk populations in East Asia. Despite these strengths, our study was limited by small numbers for subgroup analyses.
In conclusion, our study did not find evidence of associations between postmenopausal estrogen levels and gastric cancer risk.