[Cancer in siblings of children with cancer].
BACKGROUND
In some rare inherited disorders, such as Li-Fraumeni syndrome, relatives of children with cancer are at increased risk of cancer. We aimed to assess relations between childhood cancer and sibling risk, and evaluate the influence of recessive conditions in cancer causation.


METHODS
We did a population-based cohort study in the Nordic countries of 42,277 siblings of 25,605 children with cancer. Children with cancer were identified from records in the five Nordic cancer registries, and their siblings from nationwide population registries. Cancers in siblings were documented through record linkage with cancer registries and compared with national incidence rates. We also assessed cancer incidence in parents to identify familial cancer syndromes.


RESULTS
284.2 cancers were expected in siblings, whereas 353 were diagnosed (standardised incidence ratio 1.24 95% CI, 1.12-1.38). Risk ratios for siblings were highest in the first decade of life (2.59; 1.89-3.46). We excluded 56 families with genetic syndromes linked to cancer, which reduced this ratio from 1.7 to 1.0 (0.7-1.3) for siblings younger than 20 years and from 1.3 to 1.0 (0.8-1.3) for those aged 20-29 years. We found no new patterns of familial cancer that indicated inherited susceptibility, or evidence that recessive conditions might contribute to cancers not explained by syndromes. 40% of cancers in siblings that occurred before age 20 years could be attributed to known genetic factors, whereas 60% remained unexplained.


CONCLUSIONS
Apart from rare cancer syndromes, paediatric cancer is not an indicator of increased risk in siblings.
Winther
Jeanette Falck
JF
Institut for Epidemiologisk Kraeftforskning, Kraeftens Bekaempelse, Strandboulevarden 49, DK-2100 København ø. jeanette@cancer.dk
Sankila
Risto
R
Boice
John D
JD
Tulinius
Hrafn
H
Bautz
Andrea
A
Barlow
Lotti
L
Glattre
Eystein
E
Langmark
Frøydis
F
Möller
Torgil
T
Mulvihill
John J
JJ
Olafsdottir
Gudridur H
GH
Ritvanen
Annukka
A
Olsen
Jørgen H
JH
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005387:Finland / Q000453:epidemiology; D020022:Genetic Predisposition to Disease; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D009369:Neoplasms / Q000453:epidemiology / Q000235:genetics*; D009679:Nuclear Family; D016017:Odds Ratio; D012042:Registries; D012307:Risk Factors; D012537:Scandinavian and Nordic Countries / Q000453:epidemiology