Persistent Variations of Blood DNA Methylation Associated with Treatment Exposures and Risk for Cardiometabolic Outcomes among Long-term Survivors of Childhood Cancer: A Report from the St. Jude Lifetime Cohort

Background: It is well-established that cancer treatment substantially increases risk of long-term adverse health outcomes among childhood cancer survivors. However, there is limited research on the underlying mechanisms. To elucidate the pathophysiology and a possible causal pathway from treatment exposures to cardiometabolic conditions, we conducted epigenome-wide association studies (EWAS) to identify DNA methylation (DNAm) sites associated with cancer treatment exposures and examined whether treatment-associated DNAm sites mediate associations between specific treatments and cardiometabolic conditions. Methods: We included 2,052 survivors (median age 33.7 years) of European ancestry from the St. Jude Lifetime Cohort Study, a retrospective hospital-based study with prospective clinical follow-up. Cumulative doses of chemotherapy and region-specific radiation were abstracted from medical records. Seven cardiometabolic conditions were clinically assessed. DNAm profile was measured using MethylationEPIC BeadChip with blood-derived DNA. Results: By performing multiple treatment-specific EWAS, we identified 2,894 59-cytosine-phosphate-guanine-39 (CpG) sites mapped to 1,583 gene/regions associated with one or more cancer treatments at epigenome-wide significance level (P9x10-8). Among the treatment-associated CpGs, 298 were associated with obesity, 85 with hypercholesterolemia, 41 with hypertriglyceridemia, and four with abnormal glucose metabolism (False-Discovery-Rate-Adjusted P<0.05). We observed full mediation by methylation at five independent CpGs for association between abdominal field radiotherapy (abdominal-RT) and risk of hypertriglyceridemia, nearly full mediation (99.5%) by methylation at nine CpGs for association between abdominal-RT and hypercholesterolemia, and partial mediation (42.1%) by methylation at two CpGs for association between abdominal-RT and abnormal glucose metabolism. In addition, six CpGs partially mediated the association between brain-RT and obesity with 58.6% mediation effect, two CpGs mediated the association between glucocorticoids and obesity (32.2%) and between brain-RT and hypertriglyceridemia (15.5%). Notably, several mediator CpGs reside in the proximity of well-established dyslipidemia genes: cg17058475 (CPT1A), cg11851174 (RAI1) and cg22976567 (LMNA). Conclusions: In childhood cancer survivors, prior cancer treatments are associated with DNAm variations present decades following the exposure. Treatment-associated DNAm sites may mediate the causal pathway from specific treatment exposures to certain cardiometabolic conditions, suggesting the utility of DNAm sites as risk predictors and potential mechanistic targets for future intervention studies.