Patients with congenital heart disease (CHD) have an increased cancer risk. The aim of this study was to determine cancer-related mortality in CHD patients compared with non-CHD controls, compare ages at cancer diagnosis and death, and explore the most fatal cancer diagnoses.

Registry-based cohort study.

CHD patients born between 1970 and 2017 were identified using Swedish Health Registers. Each was matched by birth year and sex with 10 non-CHD controls. Included were those born in Sweden with a cancer diagnosis.

Cancer developed in 758 out of 67814 CHD patients (1.1%), with 139 deaths (18.3%)—of which 41 deaths occurred in patients with genetic syndromes. Cancer was the cause of death in 71.9% of cases. Across all CHD patients, cancer accounted for 1.8% of deaths. Excluding patients with genetic syndromes and transplant recipients, mortality risk between CHD patients with cancer and controls showed no significant difference (adjusted HR 1.17; 95% CI 0.93 to 1.49). CHD patients had a lower median age at cancer diagnosis—13.0 years (IQR 2.9–30.0) in CHD versus 24.6 years (IQR 8.6–35.1) in controls. Median age at death was 15.1 years (IQR 3.6–30.7) in CHD patients versus 18.5 years (IQR 6.1–32.7) in controls. The top three fatal cancer diagnoses were ill-defined, secondary and unspecified, eye and central nervous system tumours and haematological malignancies.

Cancer-related deaths constituted 1.8% of all mortalities across all CHD patients. Among CHD patients with cancer, 18.3% died, with cancer being the cause in 71.9% of cases. Although CHD patients have an increased cancer risk, their mortality risk post-diagnosis does not significantly differ from non-CHD patients after adjustements and exclusion of patients with genetic syndromes and transplant recipients. However, CHD patients with genetic syndromes and concurrent cancer appear to be a vulnerable group.