We aimed to assess cancer risk in congenital heart defect patients, with and without Down's syndrome, compared with the general population.

We identified all patients born and diagnosed with congenital heart defects from 1977 to 2008 using the Danish National Registry of Patients, covering all Danish hospitals. We compared cancer incidence in the congenital heart defect cohort with that expected in the general population (∼5.5 million) using the Danish Cancer Registry, and computed age- and gender-standardised incidence ratios.

We identified 15,905 congenital heart defect patients, contributing a total of 151,172 person-years at risk; the maximum length of follow-up was 31 years (median 8 years). In all, 53 patients were diagnosed with cancer, including 30 female and 23 male patients (standardised incidence ratio = 1.63; 95% confidence interval: 1.22–2.13). Risks were increased for leukaemia, brain tumours, and basal cell carcinoma. After excluding 801 patients with Down's syndrome, the standardised incidence ratio was 1.19 (95% confidence interval: 0.84–1.64). In the subgroup of 5660 non-Down's syndrome patients undergoing cardiac surgery or catheter-based interventions, the standardised incidence ratio was 1.45 (95% confidence interval: 0.86–2.29).

The overall risk of cancer among congenital heart defect patients without Down's syndrome was not statistically significantly elevated. Cancer risk in the congenital heart defect cohort as a whole, including patients with Down's syndrome, was increased compared with the general population, although the absolute risk was low. Studies with longer follow-up and more information on radiation doses are needed to further examine a potential cancer risk associated with diagnostic radiation exposure.