Background: Linked population-based registries provide a unique source for identification of new family cancer syndromes and for elucidating risk of early-onset cancer in close relatives of cancer patients.
Methods: Using the Finnish Cancer Registry, we identified 9078 probands who had been diagnosed with cancer at <21 years of age between 1970 and 2012. Siblings, offspring, parents, nephews, and nieces of probands were identified from the Population Registry. Childhood and young adult (ChYA) cancer diagnoses (age 0-39 years) in relatives were identified by linking to the Finnish Cancer Registry. The relative risk of ChYA cancer in family members of probands was estimated using standardized incidence ratios (SIRs).
Results: Among 58,010 family members of the 9078 probands, 363 ChYA cancers were diagnosed, 324 of which were expected (SIR, 1.12; 95% CI, 1.01-1.24). The risk of ChYA cancer was elevated both in offspring (SIR, 2.25; 95% CI, 1.51-3.24) and in siblings (SIR, 1.17; 95% CI, 1.01-1.36). Offspring of probands with retinoblastoma were at highest risk (SIR, 75.85; 95% CI, 32.75-149.45); risks were also elevated for siblings of probands with lymphoma (SIR, 1.62; 95% CI, 1.14-2.25). Known cancer predisposition syndromes were observed in 29 (66%) of 44 sibling pairs with cancers diagnosed at <21 years of age and in 20% of the 135 families with a childhood cancer proband whose sibling was diagnosed with a young adult malignancy.
Conclusion: Linked population-based registry data indicate a modestly increased risk of ChYA in relatives of children with cancer. Some of the observed cancer clusters in the cohort suggest novel patterns and familial cancer syndromes.
Keywords: cancer predisposition; childhood; familial cancer.
© 2020 American Cancer Society.