Colorectal Cancer Risk In African Americans Research Articles

Abstract B31: Sulfidogenic bacteria are an important diet-driven exposure promoting colorectal cancer in African Americans

Abstract Objectives. Colorectal cancer (CRC) incidence is higher in post-industrial cultures, and the incidences varies among different populations. In the US, there is a higher incidence of CRC in African Americans (AAs) compared to non-Hispanic whites (NHWs). Recent evidence links consumption of a diet high in animal protein and fat as an environmental risk factor for the development of CRC. The intestinal microbiota is postulated to modulate the effects of diet in promoting or preventing CRC development. Hydrogen sulfide, which is produced by normal members of the colonic microenvironment (sulfidogenic bacteria), triggers pro-inflammatory and hyper-proliferative pathways, and it is genotoxic. We hypothesized that the production of hydrogen sulfide by sulfidogenic bacteria is a key environmental carcinogen contributing to CRC risk. Design. The abundance of sulfidogenic bacteria via quantitative PCR (qPCR) was compared in non-involved colonic mucosa of 97 AA and 56 NHW CRC patients and in 100 AA and 76 NHW healthy controls. In addition, we performed 16S rDNA sequencing in 61 AA cases and 94 AA controls. Additionally, we tested correlations among race, dietary intake, disease status, and sulfidogenic bacterial abundance. Results. Overall, the functional gene for hydrogen sulfide production in sulfate-reducing bacteria, dissimilatory sulfate reductase (dsrA), was more abundant in AAs than in NHWs, in both cases and controls. In addition, AA CRC cases exhibited a significantly higher abundance of Bilophila wadsworthia-specific dsrA. Linear discriminant analysis of 16S rDNA sequencing results revealed several taxa that differed between AA cases and controls, including the known butyrate producer Faecalibacterium that was more abundant in AA controls, and the sulfidogenic Pyramidobacter that was more abundant in AA CRC cases. Importantly, we found that dietary intake of protein and fat was higher in AAs compared to NHWs, and these dietary components correlated with a higher abundance of sulfidogenic bacteria. Conclusion. There were significant differences in sulfidogenic bacterial abundance between AAs and NHWs, in both cases and controls, and implicate sulfidogenic bacteria as an important diet-driven environmental exposure that contributes to the increased risk of CRC in AAs. Replication studies are needed to test that effectiveness of using B. wadsworthia as a biomarker for increased CRC risk. Citation Format: Cemal Yazici, Patricia G. Wolf, Tzu-Wen Liu, Karin Vermillion, Timothy Carroll, Ece Mutlu, Lisa Tussing-Humphreys, Carol Braunschweig, Rosa M. Xicola, Barbara Jung, Xavier Llor, Nathan A. Ellis, H. Rex Gaskins. Sulfidogenic bacteria are an important diet-driven exposure promoting colorectal cancer in African Americans. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr B31.

Covering the Cover

Covering the Cover

Mutation Spectrum and Risk of Colorectal Cancer in African American Families with Lynch Syndrome

African Americans (AAs) have the highest incidence of and mortality resulting from colorectal cancer (CRC) in the United States. Few data are available on genetic and nongenetic risk factors for CRC among AAs. Little is known about cancer risks and mutations in mismatch repair (MMR) genes in AAs with the most common inherited CRC condition, Lynch syndrome. We aimed to characterize phenotype, mutation spectrum, and risk of CRC in AAs with Lynch syndrome. We performed a retrospective study of AAs with mutations in MMR genes (MLH1, MSH2, MSH6, and PMS2) using databases from 13 US referral centers. We analyzed data on personal and family histories of cancer. Modified segregation analysis conditioned on ascertainment criteria was used to estimate age- and sex-specific CRC cumulative risk, studying members of the mutation-carrying families. We identified 51 AA families with deleterious mutations that disrupt function of the MMR gene product: 31 in MLH1 (61%), 11 in MSH2 (21%), 3 in MSH6 (6%), and 6 in PMS2 (12%); 8 mutations were detected in more than 1 individual, and 11 have not been previously reported. In the 920 members of the 51 families with deleterious mutations, the cumulative risks of CRC at 80 years of age were estimated to be 36.2% (95% confidence interval [CI], 10.5%-83.9%) for men and 29.7% (95% CI, 8.31%-76.1%) for women. CRC risk was significantly higher among individuals with mutations in MLH1or MSH2 (hazard ratio, 13.9; 95% CI, 3.44-56.5). We estimate the cumulative risk for CRC in AAs with MMR gene mutations to be similar to that of individuals of European descent with Lynch syndrome. Two-thirds of mutations were found in MLH1, some of which were found in multiple individuals and some that have not been previously reported. Differences in mutation spectrum are likely to reflect the genetic diversity of this population.

Mo1152 The Role of Cancer Stem Cells in the Increased Risk of Colorectal Cancer in African-Americans

Background: Epidemiological studies have demonstrated that African-Americans (AAs) have a higher incidence of colorectal cancer (CRC) and greater mortality from this disease than Caucasians (CAs). The underlyingmechanisms for this increased risk are not well understood. We hypothesize that differences in the number and characteristics of a small subset of selfrenewing cancer stem/stem-like cells (CSCs) present within the colonic mucosa are responsible for the higher incidence of CRC in AAs. We also postulate that microRNAs (miRs), specifically miR-21, up-regulated in CRC and miR-145, which is down-regulated in CRC, play pivotal roles in regulating colon CSCs. Methods: Biopsies were obtained through a standardized protocol from normal-appearing colonic mucosa at the time of routine colonoscopy. Biopsies were subjected to collagenase/hyaluronidase digestion for isolation of CSCs (AJP:GI 302:G655-'63, 2012) and subsequently analyzed for CD44+CD166colon CSC phenotype, which we have previously found to be significantly higher in colonic mucosa of patients with tubular adenomas than those without adenomas (Dig. Dis. Sci. 57:2334'39, 2012). We also determined the expression of miR-21 and miR-145. In addition, the relative abundance of EGFR and β-catenin, that are known to be dysregulated in CRC, was examined by immunohistochemistry. Results: The current cohort includes 48 subjects, of which 63% were found to have adenomas. We have observed a 44.7% higher proportion of CD44+/CD166CSC phenotype in normal appearing colonic mucosa in AAs (27.12%; n=10) than CAs (18.74%; n=8). Likewise, the levels of miR-21 were 70% higher in the colonic mucosa of AAs with adenomas than CAs. In contrast, miR-145 levels were downregulated by 45% in AAs over the CA patients. The relative abundance of both EGFR and β-catenin in the colonic crypt of AAs was found to be 80% and 5-fold higher, respectively in AAs with adenomas than their CA counterparts. Conclusion: The increased risk for CRC in AAs might be explained by the increase CSCs in their colonic mucosa. miR-21 and miR-145, which also regulate EGFR, are thought to be involved in regulating CSCs in the colonic mucosa of AAs.

Mo1154 3D Reconstruction of Stomach Using Endoscopy for Endoluminal Bariatric Treatment

Background: Epidemiological studies have demonstrated that African-Americans (AAs) have a higher incidence of colorectal cancer (CRC) and greater mortality from this disease than Caucasians (CAs). The underlyingmechanisms for this increased risk are not well understood. We hypothesize that differences in the number and characteristics of a small subset of selfrenewing cancer stem/stem-like cells (CSCs) present within the colonic mucosa are responsible for the higher incidence of CRC in AAs. We also postulate that microRNAs (miRs), specifically miR-21, up-regulated in CRC and miR-145, which is down-regulated in CRC, play pivotal roles in regulating colon CSCs. Methods: Biopsies were obtained through a standardized protocol from normal-appearing colonic mucosa at the time of routine colonoscopy. Biopsies were subjected to collagenase/hyaluronidase digestion for isolation of CSCs (AJP:GI 302:G655-'63, 2012) and subsequently analyzed for CD44+CD166colon CSC phenotype, which we have previously found to be significantly higher in colonic mucosa of patients with tubular adenomas than those without adenomas (Dig. Dis. Sci. 57:2334'39, 2012). We also determined the expression of miR-21 and miR-145. In addition, the relative abundance of EGFR and β-catenin, that are known to be dysregulated in CRC, was examined by immunohistochemistry. Results: The current cohort includes 48 subjects, of which 63% were found to have adenomas. We have observed a 44.7% higher proportion of CD44+/CD166CSC phenotype in normal appearing colonic mucosa in AAs (27.12%; n=10) than CAs (18.74%; n=8). Likewise, the levels of miR-21 were 70% higher in the colonic mucosa of AAs with adenomas than CAs. In contrast, miR-145 levels were downregulated by 45% in AAs over the CA patients. The relative abundance of both EGFR and β-catenin in the colonic crypt of AAs was found to be 80% and 5-fold higher, respectively in AAs with adenomas than their CA counterparts. Conclusion: The increased risk for CRC in AAs might be explained by the increase CSCs in their colonic mucosa. miR-21 and miR-145, which also regulate EGFR, are thought to be involved in regulating CSCs in the colonic mucosa of AAs.

Abstract 1330: Genetic variation in the vitamin D pathway and risk for colorectal cancer in African Americans.

Abstract Background: Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in both sexes in the United States. There is a large disparity in both CRC incidence and survival between African Americans (AAs) and all other US racial groups. Differences in serum vitamin D levels could contribute to this disparity because vitamin D is thought to protect against CRC and AAs have lower serum vitamin D levels than whites. We hypothesized that genetic variants in vitamin D-related genes are associated with CRC risk in AAs. Methods: To evaluate association with CRC risk, we genotyped 39 putatively functional single nucleotide polymorphisms (SNPs) in vitamin D-related genes (CYP27A1, GC, CYP3A4, CYP2R1, DHCR7/NADSYN1, VDR, CYP27B1 and CYP24A1, in 961 AA cases (292 right colon, 340 left colon, 113 rectal) and 838 AA controls from the North Carolina Colorectal Cancer Study and the Chicago Colorectal Cancer Consortium. We calculated odds ratios (OR) using logistic regression, assuming an additive genetic model and controlling for age, gender, and West African ancestry. We further evaluated whether the genetic polymorphisms conferred differential risk for right-sided CRC (R-CRC) and left-sided CRC (L-CRC, including rectal). Results: Nominal associations (p<0.05) were detected between CRC and SNPs in the 24-hydroxylase gene CYP24A1, rs73913755 (OR, 0.73; P = 0.0003), which degrades calcidiol, and the 25-hydroxylase gene CYP2R1, rs12794714 (OR, 0.82; P = 0.032), which converts cholecalciferol into calcidiol. When we analyzed R-CRC and L-CRC separately, no SNPs were associated with R-CRC, whereas 4 SNPs were associated with L-CRC. Two SNPs in the vitamin D binding protein gene GC, rs1155563 (OR, 0.77; P = 0.039) and rs16847024 (OR, 1.56; P = 0.003) and two SNPs in the 24-hydroxylase gene CYP24A1, rs6022990 (OR, 1.48; P = 0.006) and rs73913755 (OR, 0.67; P = 0.0002). The P value for rs73913755 was statistically significant after adjustment for multiple testing. Conclusion: Our results indicate that several SNPs in the vitamin D pathway contribute to CRC susceptibility in AAs. The minor allele of rs73913755 was present in at least one dose in 48% of AA controls and only 30% of cases, conferring increased protection against L-CRC. We hypothesize that the minor allele of rs73913755 causes a reduction in the expression levels of CYP24A1. Because rs73913755 is African-specific, showing high Fst value in comparison to ancestrally European populations, its presence could explain in part the lower proportion of L-CRC in AAs compared to whites. Future studies include analysis of vitamin D pathway gene expression levels relative to genotype and analysis of possible gene-vitamin D level interactions in AA CRC. Citation Format: Fabio Pibiri, Nathan Ellis, Rick Kittles, Xavier LLor, Rosa Xicola, Sonia Kupfer, Robert S. Sandler, Temitope Keku. Genetic variation in the vitamin D pathway and risk for colorectal cancer in African Americans. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1330. doi:10.1158/1538-7445.AM2013-1330

Abstract PR02: Genetic variation in the vitamin D pathway and risk for colorectal cancer in African Americans.

Abstract Background: Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in both sexes in the United States. There is a large disparity in both CRC incidence and survival between African Americans (AAs) and all other US racial groups. Differences in serum vitamin D levels could contribute to this disparity because vitamin D is thought to protect against CRC and AAs have lower serum vitamin D levels than whites. We hypothesized that genetic variants in vitamin D-related genes are associated with CRC risk in AAs. Methods: To evaluate association with CRC risk, we genotyped 39 putatively functional single nucleotide polymorphisms (SNPs) in vitamin D-related genes (CYP27A1, GC, CYP3A4, CYP2R1, DHCR7/NADSYN1, VDR, CYP27B1 and CYP24A1, in 961 AA cases (292 right colon, 340 left colon, 113 rectal) and 838 AA controls from the North Carolina Colorectal Cancer Study and the Chicago Colorectal Cancer Consortium. We calculated odds ratios (OR) using logistic regression, assuming an additive genetic model and controlling for age, gender, and West African ancestry. We further evaluated whether the genetic polymorphisms conferred differential risk for right-sided CRC (R-CRC) and left-sided CRC (L-CRC, including rectal). Results: Nominal associations (p<0.05) were detected between CRC and SNPs in the 24-hydroxylase gene CYP24A1, rs73913755 (OR, 0.73; P = 0.0003), which degrades calcidiol, and the 25-hydroxylase gene CYP2R1, rs12794714 (OR, 0.82; P = 0.032), which converts cholecalciferol into calcidiol. When we analyzed R-CRC and L-CRC separately, no SNPs were associated with R-CRC, whereas 4 SNPs were associated with L-CRC. Two SNPs in the vitamin D binding protein gene GC, rs1155563 (OR, 0.77; P = 0.039) and rs16847024 (OR, 1.56; P = 0.003) and two SNPs in the 24-hydroxylase gene CYP24A1, rs6022990 (OR, 1.48; P = 0.006) and rs73913755 (OR, 0.67; P = 0.0002). The P value for rs73913755 was statistically significant after adjustment for multiple testing. Conclusion: Our results indicate that several SNPs in the vitamin D pathway contribute to CRC susceptibility in AAs, with the minor allele of rs73913755 conferring increased protection against L-CRC. We hypothesize that the minor allele of rs73913755 causes a reduction in the expression levels of CYP24A1. We further hypothesize that there is a gradient of expression levels of CYP24A1 in the colon with higher levels on the left side than on the right side. The protective effect of rs73913755 would then be explained by increased levels of calcidiol in the tissue in combination with a threshold effect. Because rs73913755 is African-specific, its presence could explain in part the lower proportion of L-CRC in AAs compared to whites. Future studies include analysis of vitamin D pathway gene expression levels relative to genotype and analysis of possible gene-vitamin D level interactions in AA CRC. This abstract is also presented as Poster B72. Citation Format: Fabio Pibiri, Rick A. Kittles, Robert S. Sandler, Temitope O. Keku, Sonia S. Kupfer, Rosa Xicola, Xavier Llor, Nathan A. Ellis. Genetic variation in the vitamin D pathway and risk for colorectal cancer in African Americans. [abstract]. In: Proceedings of the Fifth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2012 Oct 27-30; San Diego, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(10 Suppl):Abstract nr PR02.

Abstract PL08-02: Fine mapping of genetic associations in African American colorectal cancer

Abstract Genome-wide association studies (GWAS) of colorectal cancer (CRC) have identified risk variants in 14 genomic regions through the study of Europeans with CRC. In genotype analysis of a European American CRC case-control group, effects sizes and directions of association for 24 SNPs tested, which localize to 10 of the 14 previously identified regions, were consistent with GWAS results; in contrast, in an African American CRC case-control group, the associations ran in the opposite direction for 9 of 22 SNPs tested, indicating significant genetic heterogeneity in CRC associations in African Americans compared to European Americans. We conclude that genetic markers that identify CRC risk in persons of European ancestry do not identify CRC risk in African Americans. Two hypotheses may explain the genetic heterogeneity between European and African Americans: (i) The risk alleles in both populations are the same, however, the genetic architecture differs such that other SNPs that are linked to these same risk alleles will make better markers for African American CRC risk. (ii) The underlying risk alleles are different between the two populations. A corollary of this hypothesis is that the allele frequencies of the risk alleles must be low (<5%), because most the frequent genetic polymorphisms are shared between European and African populations. Distinguishing these hypotheses is important because genetic risk associated with rare alleles could have larger effect sizes (ORs>2, for example), which could make genetic risk modeling more determinative. Furthermore, identification of multiple rare alleles, each with a moderate risk effect, could explain the missing heritability problem. To address these hypotheses, we have drilled down on each of the genetic regions identified in the European GWAS using systematic genotyping and deep re-sequencing in African American CRC cases and population-matched controls. Analysis of tagSNPs in two genes so far analyzed, GREM1 and BMP4, have demonstrated multiple, independent SNP associations, which are not correlated with SNPs previously identified in persons of European descent. Because novel SNP associations are detected in each of these genes, we suggest that rare alleles underlie these genetic risk associations. We are presently using the deep re-sequencing analysis to identify candidate risk variants, which we will then test in functional studies. Ultimately, the analysis will permit better quantification of CRC risk, and it may lead to risk assessment models that can be used clinically for screening and surveillance. Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):PL08-02.

Racial differences in colorectal cancer incidence and mortality in the Women's Health Initiative.

Colorectal cancer (CRC) incidence and mortality rates are higher in African-Americans as compared with other racial/ethnic groups. The women's health initiative (WHI) study sample was used to determine whether differences in CRC risk factors explain racial/ethnic differences in incidence and mortality. The WHI is a longitudinal study of postmenopausal women recruited from 40 centers. Baseline questionnaires were used to collect sociodemographic and health status information. All CRC diagnoses were centrally adjudicated. Cox regression models were used to compute hazard ratios (HRs) and 95% confidence intervals (CIs) for invasive CRC by race/ethnicity. The study sample included 131,481 (83.7%) White, 14,323 (9.1%) African-American, 6,362 (4.1%) Hispanic, 694 (0.4%) Native American and 4,148 (2.6%) Asian/Pacific Islanders. After a mean follow-up of 10.8 years (SD 2.9), CRC incidence was the highest in African-Americans (annualized rate = 0.14%), followed by Whites and Native Americans (0.12% each), Asian/Pacific Islanders (0.10%), and Hispanics (0.08%). After adjustment for age and trial assignment, Hispanics had a lower risk compared with Whites, HR 0.73 (95% CI: 0.54-0.97) (P = 0.03), and African-Americans had a marginally greater risk, HR 1.16 (95% CI: 0.99-1.34), P = 0.06. Multivariable adjustment attenuated the difference in incidence between African-Americans and Whites (HR 0.99, 95% CI: 0.82-1.20), while strengthening the lower HR for Hispanics (HR 0.68, 95% CI: 0.48-0.97). African-American/White differences in CRC risk are likely due to sociodemographic/cultural factors other than race. A number of modifiable exposures could be a focus for reducing CRC risk in African-Americans.