Renal cell carcinoma and risk of second primary cancer: A Danish nationwide cohort study

To examine the risk of second primary cancer in patients with incident renal cell carcinoma (RCC).

We identified all patients diagnosed with incident RCC during 1995-2019, using population-based Danish medical registries. Patients were followed from the date of RCC diagnosis until any second primary cancer diagnosis, death, emigration, or December 31, 2019, whichever came first. We computed the absolute risk, standardized incidence ratio (SIR), and excess absolute risk of second primary cancer, with 95% confidence intervals (CIs), among patients with RCC compared to the general population.

The absolute 1- and 20-year risks of any second primary cancer were 2.8% and 17.8%, respectively. Within 1 year after RCC diagnosis, we detected 20 excess cancer cases per 1000 person-years (PY) (SIR, 2.3; 95% CI: 2.1-2.6). Moreover, we detected an additional four excess cancer cases per 1000 PY during 1 to <5 years of follow-up (SIR, 1.3; 95% CI: 1.2-1.4), and 6 per 1000 PY beyond 5 years of follow-up (SIR, 1.4; 95% CI: 1.3-1.5). The sustained elevated cancer risk beyond 1 year of follow-up was mainly attributed to excess risk of lung and bladder cancer. The risk of second primary cancer was higher in 2006-2019 than in 1995-2005, but only during the first year of follow-up.

Patients with incident RCC have a sustained 40% elevated long-term risk of second primary cancer, compared with the general population. This increased risk is mainly attributed to lung and bladder cancer.