The association between serum methylmalonic acid, cobalamin-related biomarkers, and long-term mortality risk in cancer survivors: a prospective cohort study.

BACKGROUND: Elevated serum methylmalonic acid (MMA), a marker of cobalamin (vitamin B12) deficiency, has been linked to cancer progression. However, the impact of MMA or cobalamin on mortality risk in cancer survivors remains unknown.

OBJECTIVES: To explore the relationship between MMA, serum, dietary, and supplement of cobalamin, MMA metabolism-related genes, and poor prognosis in adult cancer survivors.

METHODS: We analyzed data from 1988 cancer survivors aged ≥20 y. Patients were selected from the National Health and Nutrition Examination Survey and followed up until December 31, 2019. Weighted Cox proportional hazard regression was used to estimate hazard ratios (HRs) and the corresponding 95% confidence intervals (CIs) for mortality risk assessment. Genomic analysis identified MMA metabolism-related genes linked to early death in a 33-cancer-type cohort from The Cancer Genome Atlas.

RESULTS: Among 1988 participants, 872 deaths occurred over a 10-year follow-up. Higher serum MMA levels were significantly linked to increased long-term mortality risk (tertile 3 compared with tertile 1: adjusted HR: 1.37; 95% CI: 1.11, 1.70; P-trend < 0.001). No associations were found between serum, dietary, and supplement of cobalamin and cancer survivor mortality (each P-trend > 0.143). However, MMA-associated mortality was notable in patients without deficiency. When combining cobalamin and MMA categories, multivariate-adjusted HR (95% CI) for all-cause mortality was 2.06 (95% CI: 1.60, 2.65) in participants with >250 nmol/L and cobalamin >295.1 pmol/L compared with those with MMA ≤250 nmol/L and cobalamin >295.1 pmol/L. Moreover, reduced transcriptional levels of MMA metabolism-related genes, indicating decreased mitochondrial MMA metabolism capability, are linked to an unfavorable prognosis in certain cancer types.

CONCLUSIONS: Serum MMA was associated with long-term mortality risk in adult cancer survivors, which was more significant among individuals with higher levels of serum cobalamin. These findings suggest that mortality related to MMA was attributed to the insufficient flux of MMA metabolism, not cobalamin deficiency.