The impact of African ancestry on colorectal cancer disparity.

Abstract

3621 Background: Colorectal cancer is the second leading cause of cancer deaths in the world to affect both men and women. Racial disparities have been known to affect the disease diagnosis and progression, and proliferative genomic studies have been undertaken to elucidate their relationship. In this study, we investigate the tumor mutation profile in colorectal adenocarcinoma (COAD) based on genetic ancestry using The Cancer Genetic Ancestry Atlas (TCGAA). Methods: 59 AA (African American) individuals in TCGAA COAD dataset were identified. To account for and eliminate the biases introduced by self-identification of races, we utilized TCGAA genomic analysis to accurately estimate the ancestral genomic composition of each individual. For each individual, percentages of European (EA), West African (WA), East Asian (EAA), and Native American (NA) ancestry were identified based on Local Ancestry in adMixed Populations (LAMP). Individuals were screened for dominant WA ancestry (≥50% based on LAMP) and assigned to three groups, ≥90%, 80-89%, and 50-79%. Differences in gene mutation frequency and overall survival were compared among the three subgroups of individuals with WA ancestry. Results: Based on genomic ancestry analysis, 58 individuals with dominant WA ancestry (Range 53%-100%) were identified. We classified them into three groups based on percentage of WA ancestry: ≥90% (n = 17), 80-89% (n = 26), and 50-79% (n = 15). APC was the most frequently mutated gene in all groups except ≥90% WA ancestry, which had the most mutation frequency in TP53. ≥90% WA ancestry showed the highest rate of mutation of 81.3% in TP53 compared to 70.8% (80-90% WA ancestry) and 40.0% (50-79% WA ancestry). Interestingly, ≥90% WA ancestry had the highest average rate of mutation (33%) for 7 tumor suppressor genes ( AMER1, APC, ARID1, FBXW7, TCF7L2, TGFBR2, and TP53), compared to 29% and 22% in 80-89% WA ancestry and 50-79% WA ancestry, respectively. In addition, ≥90% WA ancestry had a lower rate (19%) of mutation in 6 oncogenes ( BRAF, NRAS, KRAS, PIK3CA, SMAD4, and SOX9) compared to 24% in both 80-89% and 50-79% WA ancestry. Although not statistically significant, a higher percentage of WA ancestry in an individual was correlated with a downward trend in the overall survival rate (median survival 56.3 months in ≥90% WA ancestry vs 61.8 months in 80-89% WA ancestry). Conclusions: In this study, we analyzed different gene mutations correlated with African ancestry and their potential relationship to the etiology, progression, and prognosis of COAD. The mutation profile of these genes will allow us to investigate altered pathways associated with African ancestry and draw insight into colon cancer pathogenesis in various ancestry groups. Further studies are warranted to elucidate the role of genetic ancestry in tumorigenesis and disease progression and to identify potential therapeutic targets specific to groups disproportionately affected by cancer.