Overall, we observe that men of African over European ancestry present with longer BTLs, which concurs with data for African Americans [25]. Notably, the rate of telomere shortening with age (also known as ‘weathering’) is less pronounced for our southern African versus European Australian patients. While the latter finding may contrast with the expectation that elevated exposure to socioeconomic stressors would accelerate biological aging and as such age-associated telomere shortening in our African cohort [26], a 2019 study showed low socioeconomic status to be associated with a greater Black-White difference in age-related BTLs (5.66% longer in Black Americans), in contrast to individuals at higher socioeconomic status (2.33% longer in Black Americans) [25]. Although longer BTLs were initially marginally associated with increased PCa risk [27], more recently shorter BTLs have been associated with aggressive PCa and worse prognosis [28], with further confirmation for African American patients [29]. After adjusting for age, we found shorter BTLs to be significantly associated with aggressive disease presentation in both ancestral groups, although notably pronounced for men of European ancestry. While clinical follow-up data was not available or inconclusive for the African cohort, well-characterised follow-data was available for the European patient data. Here we found shorter BTLs (< 3200 bp) to have a strong correlation with worse prognosis after surgery. Significantly correlated with aggressive disease presentation and disease relapse, our study implicates BTL as prognostic biomarker for long-term PCa surveillance.
In contrast to BTL, African American men presented with shorter TLs than their European counterparts when derived from benign or non-cancerous formalin-fixed prostate tissue assessed using a quantitative targeted approach [30]. While assessing TLs from fresh prostate tumour tissue, here we found tumours from southern African men to present with longer telomeres. Furthermore, we found shortened African derived TTL to be associated with higher ISUP grading group or more aggressive disease at diagnosis, indicating that TL shortening is involved or even promotes PCa carcinogenesis in African men. While not associated with worse histological presentation, European PCa patients with shortened TTL showed higher risks for earlier BCR onset. We therefore speculate if shortened TTL could have substantial potential as a target for aggressive PCa therapy in African men and a prognostic biomarker of relapse in European men. Possible limitations of our study include the systematic bias of algorithms and assumption of diploidy when using the TelSeq and Computel methodologies, resulting in an overestimation of TTL as a result of polyploidy [31], with further potential impact created by varied tumour purity and sequencing coverages. Although no associations were found between TTL and all potential confounding variables tested, we appreciate that tumour heterogeneity, including our previous finding that African tumours presented with a longer-tail of cancer drivers [9], as well as our relatively small sample sizes, has the potential to lead to associated biases.
Genomic instability, defined as the acquisition of small to complex genomic variation, is a hallmark of tumourigenesis and in turn telomere shortening. Here we sought to link TTL to common variables of PCa genomic instability, from recurrently mutated cancer driver genes to our all-variant type genome-wide taxonomy. Shared between the ancestries, we found shortened TTL to be associated with acquired variation within the DNA replication tumour-associated gene SETBP1. Having previously reported SETBP1 to be significantly mutated in African-derived tumours [9], this new PCa driver [32] showing favourable outcomes in response to immune checkpoint inhibitor treatment in melanoma patients [33], warrants further investigation on the clinical impact for patients presenting with shortened TTL and SETBP1 mutant prostate tumours. European specific correlations with shortened TTL most notably included: the DNA mismatch repair gene MSH2, known to be associated with telomere shortening [34]; PTEN and TP53 tumour suppressor gene deficiencies, consistent with 2012 findings showing their critical roles in telomere dysfunction which aggravates aggressive PCa progression [35]; while the association with the newly described African-predominant PCa driver DDX11L1 [9] remains unexplained. Conversely, FOXA1 which has key roles in mediating PCa carcinogenesis and oncogenesis driven by androgen receptors [36], was the only African specific driver gene to be significantly associated with TL (defined as TL ratio). Besides SETBP1, TL driver gene associations appear to be ancestry specific with potential clinical relevance.
In addition to single oncogenic drivers, TTLs and TL ratios show significant correlations with genomic instabilities (PGA, Gain and GMS) in both Europeans positively and Africans negatively with no significant ethnic disparities observed in FDRs, where TTLs and TL ratios are robust determinants of higher levels of most types of genomic instabily (PGA, TMB, somatic SNV, somatic indel, Gain, Loss and GMS) based on P-values observed in African patients. Shorter TTLs and TL ratios are associated with elevated genomic instabilities in African men, which emphasizes the brutal roles of genomic variations in aggressive PCa in men of African ancestry [9]. Our team has generated an ancestry-defined taxonomy of PCa (GMS classification) based on all types of genomic variation, however excluding for TL data [9]. This study shows our TTL and TL ratio significantly associated with GMS subtypes and raises the TL application as additional genomic parameters for precise PCa classification in the context of ethnic differences.