PURPOSE: Solid organ (SOT) and allogeneic haematopoietic stem cell (HSCT) transplant recipients have elevated risks of de novo or secondary cancer. We explored risk factors hereof.

METHODS: Among SOT and HSCT between January 2004 and December 2014, standardised incidence ratio (SIR) of de novo/secondary cancer compared with the Danish population was determined and risk factors were identified using Poisson regression.

RESULTS: During a median of 3.4 (IQR 1.3-6.4) and 2.6 (0.8-5.4) person-years (PY) after SOT and HSCT, a total of 212/1656 (13%) and 75/992 (8%) persons developed cancer; SIR 3.61 (3.0-4.3) and 2.2 (1.6-3.0), resp.). SIR correlated with younger age and was highest for skin and haematological cancers for both types of transplantation. Within the cohort, cancer was associated with older age (adjusted incidence rate ratio > 50 vs ≤ 19 years, among SOT and HSCT: 9.4 (3.4-25.7) and 25.4 (5.1-126.0), resp.) and current elevated C-reactive protein (CRP) (≥ 10 vs < 10 mg/L: 2.5 (1.8-3.4) and 2.3 (1.4-3.9), resp.), but neither with prior cancer nor type of immunosuppressants.

CONCLUSION: Rates of de novo or secondary cancers are elevated in both SOT and HSCT compared with the general population and mainly for skin and haematological cancers. Among transplant recipients, older age and current elevated CRP are risk factors.