BackgroundEmerging evidence suggested that S-adenosylhomocysteine (SAH) may be a better serum biomarker for cardiovascular disease than homocysteine (Hcy). However, the role of SAH in hepatocellular carcinoma (HCC) prognosis remains unclear. ObjectivesWe aimed to prospectively explore the relationships between serum SAH and related metabolites (Hcy, S-adenosylmethionine [SAM]) with HCC survival, and to evaluate the effect modifications by gene polymorphisms in one-carbon metabolism key enzymes. MethodsWe included 1,080 newly diagnosed HCC patients from the Guangdong Liver Cancer Cohort. Serum SAH, Hcy, and SAM were measured utilizing HPLC-MS/MS. Gene polymorphisms in one-carbon metabolism key enzymes were identified using competitive allele-specific PCR (KASP). Primary outcomes were liver cancer-specific survival (LCSS) and overall survival (OS). Hazard ratios (HRs) and 95% confidence intervals (CIs) were computed using multivariate Cox proportional hazards models. ResultsAfter a median follow-up of 3.6 years, 601 deaths occurred, with 552 (92%) attributed to HCC. Multivariable analysis revealed that patients in the highest quartile of serum SAH concentrations were significantly associated with worse survival compared to those in the lowest quartile, with HRs of 1.58 (95% CI: 1.19, 2.10; P-trend = 0.002) for LCSS and 1.54 (95% CI: 1.18, 2.02; P-trend = 0.001) for OS. There were no significant interactions between serum SAH concentrations and genetic variants of one-carbon metabolism key enzymes. No significant associations were found between serum Hcy, SAM concentrations and SAM/SAH ratio with LCSS or OS. ConclusionsHigher serum SAH concentrations, rather than homocysteine, were independently associated with worse survival in HCC patients, regardless of the genetic variants of one-carbon metabolism key enzymes. These findings suggesting that SAH may serve as a novel metabolism-related prognostic biomarker for HCC.