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More younger siblings might bring bigger risk of brain tumors

Tuesday, December 12, 2006

December 12, 2006 (WLS) -- Being part of a large family is never easy. The more siblings you have, the more you have to deal with.

But now it seems those with many younger siblings have more to worry about. The number of younger siblings might also increase the chances of developing a brain tumor, according to a recent Swedish study published in the journal Neurology.

The study cross referenced a national family database with the national cancer registry to examine 13,613 brain tumor cases in Sweden. Researchers compared rates of brain and spinal cord tumors in each individual in the registry with the number of older and younger siblings they had. Even after adjusting for other factors, they found that the number of siblings had an effect on the risk of developing tumors.

"The most interesting findings of our study were the increased risks of childhood [brain and spinal cord cancer] found for the total number of siblings and the number of younger siblings," the authors of the study said. The researchers went on to say the risks were two times higher for those who had three or more younger siblings. Some experts said, however, that the study should not raise any alarm bells due to its many limitations.

The increased risk that the study mentions has to be put in perspective, according to Charles Poole from the department of epidemiology at the University of North Carolina's School of Public Health.

Poole said that since the risk of brain or spinal cord cancer is so low to begin with -- less than three out of 100,000 children suffer from it -- a twofold or even fourfold increase in risk is still negligible. The lifetime risk of being diagnosed with a primary brain tumor is less than 1 percent in males and females.

Other experts say the study is further limited.

"This is just not good science," said Dr. Joseph M. Piepmeier, professor of neurosurgery and director of surgical neuro-oncology at the Yale University School of Medicine.

"Another way of presenting this data is to claim that having older siblings protects the younger ones from tumors," he said. "As you can see, this gets confusing."

Infections May Be to Blame

It seems that the study raises some important questions, however. Most important, though, is why might those with many siblings be at higher risk?

According to the authors of the study, the number of siblings is an indicator of early-life exposure to infections. When children come in close contact with one another, they share exposures to many infectious agents.

By some estimates, infections rank only below tobacco and diet as leading causes of cancer worldwide, according to the Harvard Center for Cancer Prevention at the Harvard School of Public Health.

Certain infections can either directly or indirectly lead to cancer, according to the Center.

When the body reacts to viruses and other intruders, it may cause certain cells of the body to change. When this happens over and over again, the result can sometimes be uncontrolled growth -- one of the steps that could lead to cancer.

Some cancers of the cervix, liver, stomach and other areas have been linked to infections.

However, when it comes to a link between infections and brain and spinal cord cancers, there is still debate.

"There are no verified reports of infection as a cause of brain tumors," said Dr. Martin H. Weiss, professor and chairman of neurological surgery at the University of Southern California. "For that matter, people who sustain an infection of the brain -- such as meningitis -- have a better prognosis in the face of a malignant brain tumor, presumably due to enhanced immune response."

This "protective" effect seems to be borne out in the findings of the study. Researchers saw a small decrease in risk of brain and spinal cord tumors with the number of older siblings. This suggests that exposure to infections (from the older sibling) around the time of birth may be beneficial.

But experts agree that there are too few previous studies to claim consistency. They said that based on these preliminary findings, however, it is clear that more studies on brain tumors and the possibility that some of them are caused by infectious agents need to be done.

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