Gene scan shows childhood brain cancer is different

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WASHINGTON: A study of the genetic map of brain tumors in children shows they have many fewer mutations than similar tumors in adults -- meaning it may someday be easier to treat them, researchers reported on Thursday.

The study of medulloblastoma, the most common type of brain cancer in children, also turned up some new mutations, the researchers reported in the journal Science.

"These analyses clearly show that genetic changes in pediatric cancers are remarkably different from adult tumors," Dr. Victor Velculescu of Johns Hopkins University in Baltimore, whose team led the study, said in a statement.

"With fewer alterations, the hope is that it may be easier to use the information to develop new therapies for them."

Medulloblastoma is the most common malignant brain tumor in children, diagnosed in about 400 children a year in the United States, with a survival rate of 70 percent and higher.

"It's a particular challenge to treat children with brain cancer because our most effective treatments, surgery and radiation therapy, can cause significant side effects, including cognitive disabilities and hormone abnormalities," said Dr. Donald Parsons of the Baylor College of Medicine in Texas.

"For our youngest patients, the effects can be potentially devastating."

The researchers sequenced nearly all the genes in tumors taken from 22 children with medulloblastoma and compared them with normal DNA. Each tumor sample had an average of 11 mutations, the researchers said, and they found 225 different mutations in all.

They compared these findings to samples from 66 other medulloblastoma tumors, including some samples from adults.

They found some of the expected gene mutations. In 16 percent of the patients they found new and unexpected mutations in the MLL2 and MLL3 genes, genes known to help suppress tumors that were not previously implicated in medulloblastoma.

"Like other genes found in medulloblastoma, the MLL2 and MLL3 genes disrupt normal brain development during childhood," Dr. Peter Phillips of The Children's Hospital of Philadelphia said in a statement.

"These genes interfere with biological signals during development."

Targeted therapies that kill cells with known cancer-causing mutations are becoming more common in cancer treatment and it may be possible to design drugs that can treat childhood brain tumors with fewer side effects than current approaches, the researchers said.

"Now, we must figure out how to put the puzzle together and zero in on parts of the puzzle to develop new therapies," Dr. Bert Vogelstein of Johns Hopkins said in a statement. "This is what scientists will be focused on for the next decade."

The researchers said they would also investigate whether mutations in other genes involved in development, such as the MLL genes, were involved in other types of childhood cancer.

Last week a team at St. Jude Children's Research Hospital in Memphis, Tennessee, and an international team of colleagues found medulloblastomas could be divided into two different types of cancer, and suggested the youngest patients could receive less toxic treatments.