Cancer sequencing initiative discovers mutations tied to aggressive childhood brain tumors

Researchers studying a rare, lethal childhood tumor of the brainstem discovered that nearly 80 percent of the tumors have mutations in genes not previously tied to cancer. Early evidence suggests the alterations play a unique role in other aggressive pediatric brain tumors as well.

The findings from the St. Jude Children's Research Hospital – Washington University Pediatric Cancer Genome Project (PCGP) offer important insight into a poorly understood tumor that kills more than 90 percent of patients within two years. The tumor, diffuse intrinsic pontine glioma (DIPG), is found almost exclusively in children and accounts for 10 to 15 percent of pediatric tumors of the brain and central nervous system.

"We are hopeful that identifying these mutations will lead us to new selective therapeutic targets, which are particularly important since this tumor cannot be treated surgically and still lacks effective therapies," said Suzanne Baker, Ph.D., co-leader of the St. Jude Neurobiology and Brain Tumor Program and a member of the St. Jude Department of Developmental Neurobiology. She is a corresponding author of the study published in the January 29 online edition of the scientific journal Nature Genetics.

DIPG is an extremely invasive tumor that occurs in the brainstem, which is at the base of the skull and controls such vital functions as breathing and heart rate. DIPG cannot be cured by surgery and is accurately diagnosed by non-invasive imaging. As a result, DIPG is rarely biopsied in the U.S. and little is known about it.

Cancer occurs when normal gene activity is disrupted, allowing for the unchecked cell growth and spread that makes cancer so lethal. In this study, investigators found 78 percent of the DIPG tumors had alterations in one of two genes that carry instructions for making proteins that play similar roles in packaging DNA inside cells. Both belong to the histone H3 family of proteins. DNA must be wrapped around histones so that it is compact enough to fit into the nucleus. The packaging of DNA by histones influences which genes are switched on or off, as well as the repair of mutations in DNA and the stability of DNA. Disruption of any of these processes can contribute to cancer.

Researchers said that the mutations seem unique to aggressive childhood brain tumors.

"It is amazing to see that this particular tumor type appears to be characterized by a molecular 'smoking gun' and that these mutations are unique to fast-growing pediatric cancers in the brain," said Richard K. Wilson, Ph.D., director of The Genome Institute at Washington University School of Medicine in St. Louis and one of the study's corresponding authors. "This is exactly the type of result one hopes to find when studying the genomes of cancer patients."

The results are the latest from the PCGP, an ambitious three-year effort to sequence the complete normal and cancer genomes of 600 children with some of the most poorly understood and aggressive pediatric cancers. The human genome includes the complete set of instructions needed to assemble and sustain human life. The goal is to identify differences that explain why cancer develops, spreads and kills. Researchers believe the findings will provide the foundation for new tools to diagnose, treat or prevent the disease.