Research on esophageal cancer: With personal perspectives from studies in China and Kenya

The most common form of esophageal cancer (EC), esophageal squamous cell carcinoma (ESCC), is prevalent in many unindustrialized societies, among people with lower socioeconomic status and those who frequently use tobacco and alcohol. In some areas, ESCC mortality ranked top among all cancer. In this review, we begin with discussions of the extensive research on EC in Linxian in northern China that started 60 years ago and the recent studies in Kenya from our personal perspectives. Based on the results obtained from these studies and information from the literature, we summarize our current understanding about the risk factors for ESCC including lifestyle factors (smoking, alcohol, consumption of food and beverages at high temperature and other unhealthy habits), poor diet and nutritional insufficiencies and genetic susceptibility. Elimination or minimization of these environmental risk factors, as well as early detection and treatment of precancerous lesions, would be effective means for the prevention of ESCC. Current knowledge of molecular alterations in ESCC (gene mutations, hypermethylation and amplification or overexpression), as well as treatment of ESCC and the potential of targeted therapy, are also discussed. Finally, we propose effective approaches for the prevention of ESCC by adapting a healthy lifestyle, including a healthy diet that would also prevent other diseases. Community outreach, public education and international collaboration are important for achieving this public health goal.

Genetic variants in the human leukocyte antigen region and survival of Chinese patients with non-small cell lung carcinoma

Human leukocyte antigen (HLA) is highly polymorphic, driving antigen presentation, complement cascade and leukocyte maturation against cancer cells. Therefore, we extracted genotyping data in the HLA region from an ongoing Chinese genome-wide association study of non-small cell lung cancer (NSCLC). Using deep sequencing data of 10 689 healthy Han Chinese, we imputed for untyped genetic variants in the HLA region, followed by a two-stage survival analysis of 1531 NSCLC patients. In the discovery stage of 758 patients, we identified 301 out of 15 138 single-nucleotide polymorphisms to be independently associated with overall survival [P < 0.05 and Bayesian false-discovery probability < 0.8]. In further validation of another 773 patients, we confirmed chromosome 6p21, rs241424 (located at intron 3 of TAP2) and rs6457642 as two independent survival predictors. In the combined analysis of 1531 NSCLC patients, rs241424 G>A and rs6457642 C>T were associated with a hazards ratio of 1.26 [95% confidence interval (CI) = 1.14-1.40 and P = 4.04 × 10-6] and 0.76 (95% CI = 0.66-0.87 and P = 1.16 × 10-4), respectively. The analysis of publically available ChIP-sequencing and Hi-C data found that the rs241424 locus was involved in potential cis-regulatory element by a long-range interaction with the HLA-DQA1 promoter. Additional expression quantitative trait loci analysis showed that the rs241424 G>A change decreased HLA-DQA1 mRNA expression. Furthermore, expression levels of HLA-DQA1 were lower in lung cancer tissues than in adjacent normal tissues, and the lower expression was associated with a worse prognosis for patients with lung adenocarcinoma. Collectively, HLA genetic variants may modulate OS of NSCLC patients, possibly via a mechanism of long-range promoter interaction regulating HLA-DQA1 expression.

Meta-analysis of genome-wide association studies and functional assays decipher susceptibility genes for gastric cancer in Chinese populations

OBJECTIVE

Although a subset of genetic loci have been associated with gastric cancer (GC) risk, the underlying mechanisms are largely unknown. We aimed to identify new susceptibility genes and elucidate their mechanisms in GC development.

DESIGN

We conducted a meta-analysis of four genome-wide association studies (GWASs) encompassing 3771 cases and 5426 controls. After targeted sequencing and functional annotation, we performed in vitro and in vivo experiments to confirm the functions of genetic variants and candidate genes. Moreover, we selected 33 promising variants for two-stage replication in 7035 cases and 8323 controls from other five studies.

RESULTS

The meta-analysis of GWASs identified three loci at 1q22, 5p13.1 and 10q23.33 associated with GC risk at p<5×10^-8 and replicated seven known loci at p<0.05. At 5p13.1, the risk rs59133000[C] allele enhanced the binding affinity of NF-κB1 (nuclear factor kappa B subunit 1) to the promoter of PRKAA1, resulting in a reduced promoter activity and lower expression. The knockout of PRKAA1 promoted both GC cell proliferation and xenograft tumour growth in nude mice. At 10q23.33, the rs3781266[C] and rs3740365[T] risk alleles in complete linkage disequilibrium disrupted and created, respectively, the binding motifs of POU2F1 and PAX3, resulting in an increased enhancer activity and expression of NOC3L, while the NOC3L knockdown suppressed GC cell growth. Moreover, two new loci at 3q11.2 (OR=1.21, p=4.56×10^-9) and 4q28.1 (OR=1.14, p=3.33×10^-11) were associated with GC risk.

CONCLUSION

We identified 12 loci to be associated with GC risk in Chinese populations and deciphered the mechanisms of PRKAA1 at 5p13.1 and NOC3L at 10q23.33 in gastric tumourigenesis.