Integrative Omics Analysis Reveals Functional Variants of Hemoglobin Zeta (HBZ) as an Ancestry-Specific Risk Factor for Triple-Negative Breast Cancer

Background: Triple-negative breast cancer (TNBC) disproportionately affects women of African ancestry, yet the biological mechanisms underlying this disparity remain poorly understood. While recent genome-wide association studies (GWAS) have identified numerous TNBC risk variants, their functional consequences have not been systematically evaluated in African-ancestry populations. We hypothesized that ancestry-specific regulatory variants drive distinct transcriptomic and proteomic landscapes that contribute to TNBC aggressiveness. Methods: We extracted 2,849 unique TNBC-associated variants (p-value [≤] 0.0001) from the GWAS Catalog. Of these, 206 were excluded due to absence in our whole-genome sequencing (WGS) dataset or low minor allele frequency ([≤] 0.01). We prioritized the remaining 2,643 bi-allelic variants for analysis in the GENE-FORECAST cohort. We integrated WGS with whole-blood transcriptomic (n=242) and proteomic data (n=362) to perform cis-eQTL and cis-pQTL analyses in discovery and validation sets. Results: We identified 38 cis-eQTL associations and 5 cis-pQTL associations that were statistically replicated across independent discovery and validation datasets within our cohort. Both omics layers converged on a single gene, Hemoglobin Zeta (HBZ). We identified five functional variants (four SNPs and one INDEL) in strong linkage disequilibrium that consistently upregulate HBZ mRNA and the corresponding circulating embryonic zeta-globin protein. These variants were found almost exclusively in African and African-admixed populations across GENE-FORECAST, 1000 Genomes, BioVU, and All of Us datasets. Four of the five variants were also confirmed as significant HBZ eQTLs in GTEx whole blood. Conclusion: Our integrative analysis reveals variants of the embryonic HBZ gene as a novel, ancestry-specific TNBC-associated risk factor that is detectable at both transcriptomic and proteomic levels. This suggests that aberrant reactivation of this embryonic globin may provide a selective advantage in the hypoxic TNBC microenvironment. These results highlight a unique mechanism of tumorigenesis in women of African ancestry, offering a potential distinct biomarker and therapeutic target for this high-risk population.