Comparing causes of death of Hodgkin lymphoma and breast cancer patients between medical records and cause-of-death statistics

OBJECTIVE: Obtaining accurate data about causes of death may be difficult in patients with a complicated disease history, including cancer survivors. This study compared causes of death derived from medical records (COD(MR)) with causes of death derived from death certificates (COD(DC)) as processed by Statistics Netherlands of patients primarily treated for Hodgkin lymphoma (HL) or breast cancer (BC). METHODS: Two hospital-based cohorts comprising 1,215 HL patients who died in the period 1980–2013 and 714 BC patients who died in the period 2000–2013 were linked with cause-of-death statistics files. The level of agreement was assessed for common underlying causes of death using Cohen’s kappa, and original death certificates were reviewed when COD(DC) and COD(MR) showed discrepancies. We examined the influence of using COD(DC) or COD(MR) on standardized mortality ratio (SMR) estimates. RESULTS: Agreement for the most common causes of death, including selected malignant neoplasms and circulatory and respiratory diseases, was 81% for HL patients and 97% for BC patients. HL was more often reported as COD(DC) (COD(DC)=33.1% vs. COD(MR)=23.2%), whereas circulatory disease (COD(DC)=15.6% vs. COD(MR)=20.9%) or other diseases potentially related to HL treatment were more often reported as COD(MR). Compared to SMRs based on COD(DC), SMRs based on COD(MR) complemented with COD(DC) were lower for HL and higher for circulatory disease. CONCLUSION: Overall, we observed high levels of agreement between COD(MR) and COD(DC) for common causes of death in HL and BC patients. Observed discrepancies between COD(MR) and COD(DC) frequently occurred in the presence of late effects of treatment for HL.