Abstract A34: The genetic etiology of esophageal cancer in South African Black populations

Abstract

Abstract Esophageal squamous cell carcinoma (ESCC) is common in Black populations of the sub-Saharan Africa, with high incidence regions in East and South Africa. Clinical presentation in Africa is late, and treatment is mainly palliative with a very poor prognosis. Various environmental risk factors have been identified, but the possible contribution of genetics to disease risk is an important question, which is unresolved. The aim of this project is to test the hypothesis that genetic variation in the South African Black population contributes significantly to the risk of ESCC. We have begun by testing genetic risk factors for ESCC which were identified by genome-wide association scans in other populations for association with ESCC in the South African Black population. Cases with a histologically confirmed diagnosis of ESCC and population controls were recruited, with informed consent and institutional ethical approval. All individuals were from the Black population of the Western Cape, with 98.2% being from the Xhosa ethnic group. A total of 513 ESCC cases and 820 controls were genotyped for 15 single nucleotide polymorphisms (SNPs) by validated TaqMan assays on a 7900HT (Applied Biosystems). SNPs were tested for association using an allelic chi-square test; odds ratios (OR) and 95% confidence intervals (CI) used the common allele as reference. A significance threshold of p=0.0033 was applied, from a Bonferroni multiple testing correction for 15 SNPs. No significant evidence of association was observed for the index SNPs at the previously reported loci ATP1B2, CASP8, c20orf54, HEATR3, PDE4D, PLCE1, PTPN2, RUNX1, SMG6, ST6GAL1, TMEM173 and UNC5L loci. However, the SNP rs2239815 at XBP1 on chromosome 22q12 was associated with ESCC (OR =1.41, P = 0.00087), as were 2 SNPs in CHEK2, rs4822983 (OR = 1.31, P = 0.0013) and rs1033667 (OR = 1.29, P = 0.0025). These 3 SNPs are within 70kb of each other and are in partial linkage disequilibrium in African populations. Fine-mapping of this locus will be required to determine the causal gene and variant/s driving this association. The lack of association with ESCC in the Black South African population at most of the loci previously associated in Asian GWAS suggests that at least some of these may not contribute to susceptibility to ESCC in the South African population. However, expansion of samples sizes and thus statistical power is required for more definitive exclusions, and the lower level of linkage disequilibrium (LD) across African genomes may produce a negative result if the SNP which is tagging the causal variant in Asian or European populations is in weak LD with the causal SNP in African populations. In order to address these issues we are now expanding the power and density of this study by genotyping 36 SNPs from loci of interest in 1000 South African ESCC cases and 940 controls from the Johannesburg Cancer Study by mass spectrometry using the MassArray genotyping system (Agena Bioscience). Citation Format: Wenlong Carl Chen, Hannah Bye, Marco Matejcic, Robyn Kerr, Elvira Singh, Natalie J. Prescott, Cathryn M. Lewis, Chantal Babb de Villers, Iqbal Parker, Christopher G. Mathew. The genetic etiology of esophageal cancer in South African Black populations [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr A34.