Population-based registry study of relative risk of second malignant neoplasms among adult cancer patients in Finland

A population-based registry study in Finland explored the incidence of second malignant neoplasms (SMN) among adult cancer patients diagnosed with first primary cancer (FPC) in 1992-2021. During 3,867,789 person-years of follow-up, the relative SMN risk in males was not different from the FPC risk in males in the general population (SIR 1.00; 95% CI 0.99-1.01), while in women the relative SMN risk was 8% higher compared with FPC risk in women in the general population (1.08; 1.06-1.09). The highest SIRs were observed in patients aged 20-39 years at FPC diagnosis (males: SIR 2.28; 95% CI 2.06-2.52; females: 1.61; 1.50-1.73), while SIRs decreased with increasing age. Patients with lymphoid and hematopoietic tissue neoplasms and cancers of the mouth and pharynx had the highest SIRs, while patients with cancers of the male genital organs and female breast had the lowest SIRs. The authors conclude that elevated SIRs were observed in cancer patients diagnosed at an early age.