Increased risk of chronic lymphocytic leukaemia among cancer survivors in the Netherlands: increased detection, causal factors or both?

We assessed the risk of chronic lymphocytic leukaemia (CLL) following earlier primary malignancies (EPM) to explore the extent and determinants of this risk. We used the Netherlands Cancer Registry data of 1,313,232 cancer survivors who were at risk to be subsequently diagnosed with CLL between 1989 and 2008. Cancer survivors were categorized based on gender, age, time since diagnosis of EPM and type of EPM. CLL was regarded synchronous when diagnosed within 3 months after diagnosis of EPM; metachronous CLLs were those diagnosed later. Overall, we found that cancer survivors had a 90 % higher risk to be diagnosed with CLL than the general population. In the first year after diagnosis, we found a more than four-fold increased risk of CLL (standardized incidence ratio (SIR), 4.4; 95 % confidence interval (CI), 4.1-4.8); however, no increased risk was observed after excluding synchronous cases. After 1 year, the excess risk of subsequent CLL ranged from 1.2 to 1.8. An increased risk for metachronous CLL was found in prostate (SIR 1.3; 95 % CI 1.1-1.5) and squamous cell skin cancer survivors (SIR 2.3; 95 % CI 1.9-2.7). Intensive clinical checkups after/around diagnosis of the EPM seemed to be the main cause for the increased risk of CLL among cancer survivors. However, possible shared risk factors between prostate cancer and CLL and skin cancer and CLL cannot be excluded. Further clinical research aimed at CLL as subsequent primary malignancy (SPM) is warranted to elucidate possible shared biological and predisposing risk factors.