Our results should reassure childhood cancer patients and their families

Dr Jeanette Falck Winther, of the Institute of Cancer Epidemiology, Copenhagen

When all cancers were included, brothers and sisters of sick children were two to three times more likely to have cancer than the general population.

But when cancers that are known to be inherited were excluded, they faced no increased risk.

The news has been welcomed by cancer charities.

Author Dr Jeanette Falck Winther, of the Institute of Cancer Epidemiology, Copenhagen said: "Our results should reassure childhood cancer patients and their families and will be helpful for paediatricians and genetic counsellors world-wide."

The study showed that 40% of all the cancers found in people under 20 could be attributed to known genetic factors, but that 60% remained unknown.

The researchers did notice a high number of cases of leukaemia among identical twins, but said this was not apparent in siblings in general.

Good news

Dr Mary Berrington, of the Cancer Research Campaign, said the news would provide welcome reassurance to parents.

"It's good news that the siblings of most children with cancer do not appear to be at increased risk of cancer themselves, either in childhood or as adults.

"The excess cancer risk of siblings of children with cancer was attributed almost entirely to rare, known familial cancer syndromes the authors didn't identify any new patterns of cancer risk."

This study suggests there are unlikely to be any undiscovered genes that are significant causes of childhood cancer

Dr Anneke Lucassen

Dr Anneke Lucassen, head of the Imperial Cancer Research Fund's family cancer clinic in Southampton, said previous studies had suggested there were undiscovered genes causing childhood cancers, but that this report appeared to rule this out.

"This study suggests that, if you take out of the equation all the known inherited cancer predisposing syndromes, siblings of children with cancer are not at an increased risk of getting the disease.

"Previous studies suggested that there are likely to be genes we didn't yet know about that explained why brothers or sisters of childhood cancer patients might be more at risk of cancer themselves."

Dr Lucassen added: "This study suggests there are unlikely to be any undiscovered genes that are significant causes of childhood cancer."

The study is published in The Lancet.