PURPOSE In studies of men of European ancestry, rare pathogenic variants in DNA repair pathway genes have been shown to be associated with risk of aggressive prostate cancer. The contribution of rare coding variation to prostate cancer risk in men of African ancestry has not been established. METHODS We sequenced a panel of 19 DNA repair and cancer predisposition genes in 2,453 African American and 1,151 Ugandan cases and controls with prostate cancer. Rare variants were classified as pathogenic or putatively functionally disruptive and examined in association with prostate cancer risk and disease aggressiveness in gene and pathway-level association analyses. RESULTS Pathogenic variants were found in 75 of 2,098 cases (3.6%) and 31 of 1,481 controls (2.1%; odds ratio [OR], 1.82; 95% CI, 1.19 to 2.79; P = .0044), with the association being stronger for more aggressive disease phenotypes (OR, 3.10; 95% CI, 1.54 to 6.23; P = .0022). The highest risks for aggressive disease were observed with pathogenic variants in the ATM, BRCA2, PALB2, and NBN genes, with ORs ranging from approximately 4 to 15 in the combined study sample of African American and Ugandan men. Rare, nonpathogenic, nonsynonymous variants did not have a major impact on risk of overall prostate cancer or disease aggressiveness. CONCLUSION Rare pathogenic variants in DNA repair genes have appreciable effects on risk of aggressive prostate cancer in men of African ancestry. These findings have potential implications for panel testing and risk stratification in this high-risk population.

The ∼100 known PCa risk variants were shown to effectively stratify PCa risk in Ugandan men, with 10% of men having a >4-fold increase in risk. The 8q24 risk region was also found to be a major contributor to PCa risk in Ugandan men, with the African ancestry-specific risk variant rs72725854 estimated to account for 12% of PCa in this population.

The greater incidence of prostate cancer in men of African ancestry remains one of the most important unanswered health disparities globally. No established environmental/lifestyle risk factors have been identified, with the only established risk factors being age, race/ethnicity and family history, all of which implicate genetic susceptibility. GWAS have clearly validated the importance of genetic susceptibility in prostate cancer, with ~100 common risk loci identified to date which in aggregate explain 33% of the familial risk. Genetic studies in African ancestry populations have provided strong evidence for genetic factors in contributing to the greater incidence of prostate cancer in men of African ancestry. To further explore this hypothesis, we conducted a genome-wide association study (GWAS) of prostate cancer among Ugandan men. Specifically, we genotyped the Illumina OncoArray, which includes a 260K GWAS backbone, in 560 prostate cancer cases (119 with Gleason score ≥8) and 480 controls and tested the associations of 448,939 genotyped and 16,396,662 imputed variants with >1% frequency. The most statistically significant variants were observed at the 8q24 risk locus (rs72725854, OR=3.37, P=2.14x10-13). We also observed suggestive signals with 106 variants outside of known risk regions with p-values <10-5 and >10-7. Of the 104 known risk variants, 100 are polymorphic in Uganda men, of which, 66 (66%) had effects that were directionally consistent in their association with prostate cancer risk as previously reported and 8 (8%) were significantly associated with risk at p < 0.05, with the most statistically significant variants being rs16901979 at 8q24 (OR=1.45, p=0.0001) and rs1512268 at 8p21.2 (OR=1.31, p=0.0087). In addition to these findings, we will also present the results from replication testing of the most significant associations from the GWAS in the Ghana Prostate GWAS Study and the African Ancestry Prostate Cancer Consortium, as well as provide a detailed comparison of polygenic risk models of the known prostate cancer variants between these two African populations, African Africans and men of European ancestry. Citation Format: Zhaohui Du, Alexander Lubmawa, Susan Gundell, Peggy Wan, Nalukenge Cissy, Muwanga Proscovia, Lutalo Moses, Nansereko Deborah, Ndaruhutse Olivia, Katuku Molly, Lubwama Alexander, Rosemary Nassanga, Benson Masaba, Sam Kaggwa, Dan Namuguzi, Vicky Kiddu, Asiimwe Luke, Kuteesa J, Dabanja M. Henry, David Conti, Christopher A. Haiman, Stephen Watya. A genome-wide association study of prostate cancer in Uganda [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1305. doi:10.1158/1538-7445.AM2017-1305

Introduction: Prostate Cancer (PCa) risk is influenced by both rare germline pathogenic variants (GPVs) in DNA damage repair genes and common variants as measured by polygenic risk scores (PRS) however, the combined effect of GPVs and PRS on PCa risk in men of African ancestry has not been investigated. Methods: We examined the combined effect of rare GPVs and PRS on PCa risk in 1,795 PCa cases and 1,424 controls of African ancestry men from the Multiethnic Cohort, the Los Angeles Study of Aggressive Prostate Cancer, and the Uganda Prostate Cancer Study. GPVs in 19 DNA genes were defined as clinically validated missense variants and variants that alter the protein sequence. The PRS was constructed as a weighted sum of 267 established PCa risk variants. The combined effect of the PRS and GPV status on PCa risk was evaluated using logistic regression models adjusting for age, study, and the first 10 principal components of ancestry to account for population stratification. Results: We identified 91 GPVs carried by 31 controls and 68 cases. Among GPV non-carriers, compared to those with average PRS (33.3-66.7%), odds ratios for PCa ranged from 0.56 (95% CI=0.45-0.70; P=1.2E-7) in low PRS men (0-33.3%) to 3.04 (95% CI=2.54-3.63; P=5.6E-35) in high PRS men (66.7-100%). Among GPV carriers, odds ratios for PCa ranged from 2.09 (95% CI=0.85-5.12; P=0.11) in low PRS men to 5.03 (95% CI=2.37-10.66; P=2.5E-5) in high PRS men, compared to GPV non-carriers with average PRS. Next, we restricted GPVs to ATM, BRCA2, PALB2, and NBN[BD2] (n=51 variants carried by 8 controls and 44 cases), which we previously reported as being the genes most strongly associated with advanced PCa in this population and study sample. Among GPV non-carriers, odds ratios for PCa ranged from 0.56 (95% CI=0.46-0.71; P=2.7E-7) in low PRS men to 5.03 (95% CI=0.85-5.12; P=0.11) in high PRS men, while among GPV carriers, odd ratios for PCa ranged from 2.08 (95% CI=0.58-7.49; P=0.26) in low PRS men to 18.06 (95% CI=4.24-76.84; P=9.0E-5) in high PRS men, compared to average PRS GPV non-carriers. When comparing aggressive cases to controls, considering the top four genes, GPV non-carrier odds ratios for PCa ranged from 0.52 (95% CI=0.40-0.70; P=6.2E-6) in low PRS men to 3.16 (95% CI=2.56-3.91; P=1.6E-26) in high PRS men, while among GPV carriers, odd ratios for PCa ranged from 2.97 (95% CI=073-12.16; P=0.13) in low PRS men to 23.58 (95% CI=5.39-103.20; P=2.7E-5) in high PRS men, compared to average PRS GPV non-carriers. Conclusion: We found that PCa risk in African ancestry men carrying GPVs in DNA damage repair and cancer predisposition genes, particularly ATM, BRCA2, PALB2, and NBN, varied depending on an individual's PRS. This implies that to comprehensively assess genetic risk of PCa, it is important to consider both rare and common variants. These findings could have implications for risk stratification in this high-risk population and emphasize the need for larger genetic studies of PCa in African ancestry men to identify and characterize genetic risk factors in this population. Citation Format: Raymond W. Hughley, Burcu F. Darst, Marco Matejcic, Yesha Patel, Jenna Lilyquist, Steven N. Hart, Eric C. Polley, Lucy Xia, Xin Sheng, Alexander Lubmawa, Sue A. Ingles, Lynne Wilkens, Loïc L. Marchand, Stephen Watya, Fergus J. Couch, David V. Conti, Christopher A. Haiman. Combined effect of a prostate cancer polygenic risk score and germline pathogenic variants in DNA damage repair genes on prostate cancer risk in men of African ancestry [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PO-197.