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Childhood Cancer Exposes a Weak Spot

Brain tumor molecule may be target for better treatment

WEDNESDAY, Jan. 23, 2002 (HealthDayNews) -- A poorly understood type of childhood brain cancer has a unique molecule signature that may point to which therapies could best fight it, says new research.

Armed with targeted molecular treatments, doctors may be able to fight the disease without risking the side effects of prolonged and powerful radiation and chemotherapy at an early age, the study authors say.

The latest research is a collaborative effort looking at a type of childhood tumor known as medulloblastoma, the most common childhood tumor of the central nervous system. The cancer affects roughly twice as many boys as girls, and usually strikes between the ages of 5 and 10.

Medulloblastomas are highly malignant, and can spread to the spine and other parts of the body. But over the past few decades, refined treatments have increased survival rates until approximately 80 percent of children survive for five to 10 years after diagnosis.

But the therapies aren't perfect. Radiation and chemotherapy for up to a year at such a young age can lead to hearing loss, cataracts and severe learning disabilities that can leave children unable to live independently in later life.

Using DNA technology to reveal the level of activity in more than 6,000 genes in the cancer cells, the researchers analyzed samples from 42 patients with embryonal tumors, including 10 from medulloblastoma patients, and another 10 samples from non-embryonal tumors. Embryonal tumors develop from cells that exist only in a developing brain.

Led by Dr. Scott Pomeroy, an associate professor of neurology at Children's Hospital in Boston, the researchers found that increased activity of Sonic Hedgehog (SHH), a signaling molecule crucial to brain development, is linked to one type of medulloblastoma. (The molecule, identified in 1993, was named after a cartoon character.)

The findings appear in the Jan. 24 issue of Nature.

Recently developed compounds that can block the uncontrolled SHH signaling found in the tumors could potentially be used as a therapy in children with medulloblastoma, says Pomeroy.

"As compared to chemotherapy, which is non-specific and damages all cells … these very focused treatments will only work on those tumors that have that particular molecular pathway active," says Pomeroy. "We can identify that pathway using this method."

They also found that the clinical outcome of an individual child's struggle with medulloblastoma could be accurately predicted by examining the patterns of gene expression in the cancer at the time of diagnosis.

Dr. Allen Bale, director of the DNA Diagnostic Laboratory and Cancer Genetics Program at Yale University, is familiar with the findings. He says that it's important that the researchers have found a way to biologically distinguish different types of brain tumors that have previously been lumped into one group.

But more importantly, says Bale, "[they've] found a biologically meaningful way to determine which tumors respond to therapy and which tumors don't respond to therapy."

Pomeroy says that molecularly targeted therapies may not be far away. "First we have to validate the findings," he says. "Within five years, I would expect this kind of information to become useful to treating patients."

What To Do

For information on childhood brain tumors and medulloblastoma, visit the National Cancer Institute or PedBase.

While the contents are somewhat technical, you can find out more about Sonic Hedgehog from this Howard Hughes Medical Institute Web site.

SOURCES: Interviews with Scott L. Pomeroy, M.D., Ph.D., associate professor, Division of Neuroscience, Department of Neurology, Children's Hospital, Boston; Allen E. Bale, M.D., associate professor, Department of Genetics and director, DNA Diagnostic Laboratory and Cancer Genetics Program, Yale University, New Haven, Conn.; Jan. 24, 2002, Nature
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