Does breastfeeding affect the risk of gastric cancer?

A review of the epidemiology of Barrett's oesophagus and oesophageal adenocarcinoma

While the incidence rates of many cancers have decreased in past decades, the incidence of oesophageal adenocarcinoma continues to increase. The only known precursor for oesophageal adenocarcinoma is Barrett's oesophagus. Studies conducted have identified white race, male sex, GORD, cigarette smoking, obesity, and the absence of Helicobacter pylori status as risk factors for oesophageal adenocarcinoma. Other potential associations include dietary factors and the absence of non-steroidal anti-inflammatory drug use. Many individual studies have been limited by sample size and several meta-analyses have pooled data from studies to address this limitation. In this review we present a synthesis of these studies and summarize current knowledge of risk factors for both oesophageal adenocarcinoma and Barrett's oesophagus.

Genetic susceptibility factors on genes involved in the steroid hormone biosynthesis pathway and progesterone receptor for gastric cancer risk

Background

The objective of the study was to investigate the role of genes (HSD3B1, CYP17A1, CYP19A1, HSD17B2, HSD17B1) involved in the steroid hormone biosynthesis pathway and progesterone receptor (PGR) in the etiology of gastric cancer in a population-based two-phase genetic association study.

Methods

In the discovery phase, 108 candidate SNPs in the steroid hormone biosynthesis pathway related genes and PGR were analyzed in 76 gastric cancer cases and 322 controls in the Korean Multi-Center Cancer Cohort. Statistically significant SNPs identified in the discovery phase were re-evaluated in an extended set of 386 cases and 348 controls. Pooled- and meta-analyses were conducted to summarize the results.

Results

Of the 108 SNPs in steroid hormone biosynthesis pathway related genes and PGR analyzed in the discovery phase, 23 SNPs in PGR in the recessive model and 10 SNPs in CYP19A1 in the recessive or additive models were significantly associated with increased gastric cancer risk (p<0.05). The minor allele frequencies of the SNPs in both the discovery and extension phases were not statistically different. Pooled- and meta-analyses showed CYP19A1 rs1004982, rs16964228, and rs1902580 had an increased risk for gastric cancer (pooled OR [95% CI] = 1.22 [1.01–1.48], 1.31 [1.03–1.66], 3.03 [1.12–8.18], respectively). In contrast, all PGR SNPs were not statistically significantly associated with gastric cancer risk.

Conclusions

Our findings suggest CYP19A1 that codes aromatase may play an important role in the association of gastric cancer risk and be a genetic marker for gastric cancer susceptibility.

Sex hormones, hormonal interventions, and gastric cancer risk: a meta-analysis

Estrogens may influence gastric cancer risk, but published studies are inconclusive. We therefore carried out a meta-analysis addressing the associations of gastric cancer in women with menstrual and reproductive factors and with use of estrogen- and antiestrogen-related therapies. Searches of PubMed up to June, 2011 and review of citations yielded a total of 28 independent studies, including at least one exposure of interest. Random effects pooled estimates of relative risk (RR) and corresponding 95% CIs were calculated for eight exposures reported in at least five studies, including: age at menarche, age at menopause, years of fertility, parity, age at first birth, oral contraceptive use, hormone replacement therapy (HRT), and tamoxifen treatment. Longer years of fertility (RR = 0.74, 95% CI: 0.63-0.86) and HRT (RR = 0.77; 95% CI: 0.64-0.92) were each associated with decreased gastric cancer risk. Conversely, tamoxifen treatment was associated with increased risk (RR = 1.82; 95% CI: 1.39-2.38). The other five exposures were not significantly associated. Our analysis supports the hypothesis that longer exposure to estrogen effects of either ovarian or exogenous origin may decrease risk of gastric cancer. Additional studies are warranted to extend this finding and to identify the underlying mechanisms.

Menstrual and reproductive factors, exogenous hormone use, and gastric cancer risk in a cohort of women from the European Prospective Investigation Into Cancer and Nutrition

The worldwide incidence of gastric adenocarcinoma (GC) is lower in women than in men. Furthermore, cancer patients treated with estrogens have been reported to have a lower subsequent risk of GC. The authors conducted a prospective analysis of menstrual and reproductive factors, exogenous hormone use, and GC in 335,216 women from the European Prospective Investigation Into Cancer and Nutrition, a cohort study of individuals aged 35-70 years from 10 European countries. After a mean follow-up of 8.7 years (through 2004), 181 women for whom complete exposure data were available developed GC. Adjusted hazard ratios and 95% confidence intervals were estimated using Cox proportional hazards models. All statistical tests were 2-sided. Women who had ovariectomy had a 79% increased risk of GC (based on 25 cases) compared with women who did not (hazard ratio = 1.79, 95% confidence interval: 1.15, 2.78). Total cumulative years of menstrual cycling was inversely associated with GC risk (fifth vs. first quintile: hazard ratio = 0.55, 95% confidence interval: 0.31, 0.98; P(trend) = 0.06). No other reproductive factors analyzed were associated with risk of GC. The results of this analysis provide some support for the hypothesis that endogenous ovarian sex hormones lower GC incidence in women.

Reproductive and sex hormonal factors and oesophageal and gastric junction adenocarcinoma: a pooled analysis

BACKGROUND

The rapidly rising incidence and the striking male predominance are as yet unexplained features of oesophageal and gastric junction adenocarcinoma. Few and underpowered studies have examined the impact of female reproductive factors on risk of these adenocarcinomas in women. We therefore pooled data on women from four population-based case-control studies to examine the association of female reproductive and sex hormonal factors with oesophageal and gastric junction adenocarcinoma.

METHODS

Data on women from case-control studies conducted in Ireland, the United Kingdom (UK), Australia and United States of America (USA) were pooled. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for a range of reproductive factors, adjusted for age, study and major risk factors for oesophageal and gastric junction adenocarcinoma.

RESULTS

We included 218 cases and 862 controls. Among parous women, a reduced risk of oesophageal and gastric junction adenocarcinoma was found after breastfeeding (OR=0.58, 95% CI=0.37-0.92) and the risk decreased with increased duration of breastfeeding (>12 months OR=0.42, 95% CI=0.23-0.77). The endogenous reproductive factors such as parity, menstruation, history of pregnancy and the exogenous factors such as use of oral contraceptives and of hormone replacement therapy were not statistically significantly associated with oesophageal and gastric junction adenocarcinoma.

CONCLUSION

Our findings suggest that breastfeeding is associated with a decreased risk of oesophageal and gastric junction adenocarcinoma. The potential mechanism of this association warrants further investigation.