BACKGROUND: Mitochondrial mutations are commonly reported in tumours, but it is unclear whether impaired mitochondrial function per se is a cause or consequence of cancer. To elucidate this, we examined the risk of cancer in a nationwide cohort of patients with mitochondrial dysfunction.

METHODS: We used nationwide results on genetic testing for mitochondrial disease and the Danish Civil Registration System, to construct a cohort of 311 patients with mitochondrial dysfunction. A total of 177 cohort members were identified from genetic testing and 134 genetically untested cohort members were matrilineal relatives to a cohort member with a genetically confirmed maternally inherited mDNA mutation. Information on cancer was obtained by linkage to the Danish Cancer Register. Standardised incidence ratios (SIRs) were used to assess the relative risk of cancer.

RESULTS: During 7334 person-years of follow-up, 19 subjects developed a primary cancer. The corresponding SIR for any primary cancer was 1.06 (95% confidence interval 0.68-1.63). Subgroup analyses according to mutational subtype yielded similar results, for example, a SIR of 0.94 (95% CI 0.53 to 1.67) for the m.3243A>G maternally inherited mDNA mutation, cases=13.

CONCLUSIONS: Patients with mitochondrial dysfunction do not appear to be at increased risk of cancer compared with the general population.