The number of siblings also affects the risk of brain tumors

In today's world where only children are prevalent, siblings seem to be a slightly unfamiliar term. An online report in Nature magazine about the probability of siblings getting tumors is even more unimaginable to many people. This study shows that siblings may also be a factor in whether older brothers have brain tumors.

The study, led by Andrea Altieri of the German Cancer Research Center (GCRC) in Heidelberg, analyzed more than 13,600 cases of nervous system tumors using a Swedish cancer database, currently the world's largest family cancer "registry," to analyze the odds of developing a tumor using the number of siblings a person has as a proxy measure of how many infections they are exposed to. The team found that people with four or more siblings, whether they are brothers or sisters, are twice as likely to develop certain types of brain and nervous system tumors as only children. However, children with many older brothers and sisters are not as at risk.

The results suggest that transmission of infection from younger children to older siblings may somehow increase susceptibility to these cancers during late childhood.