Medulloblastoma is a rare but devastating childhood brain cancer. This cancer can spread through the spinal fluid and be deposited elsewhere in the brain or spine. Radiation therapy to the whole brain and spine, followed by an extra radiation dose to the back of the brain, prevents this spread and has been the standard of care.
However, the radiation used to treat such tumors takes a toll on the brain, damaging cognitive function, especially in younger patients whose brains are just beginning to develop.
A national study led by Washington University School of Medicine in St. Louis and St. Jude Children’s Research Hospital suggests that children with what is called “average risk medulloblastoma” can receive a radiation “boost” to a smaller volume of the brain at the end of a six-week course of radiation treatment and still maintain the same disease control as those receiving radiation to a larger area. But the researchers also found that the dose of the preventive radiation treatments given to the whole brain and spine over the six-week regimen cannot be reduced without reducing survival. Further, the researchers showed that patients’ cancers responded differently to therapy, depending on the biology of the tumors, setting the stage for future clinical trials of more targeted treatments.
Children with average risk medulloblastoma have five-year survival rates of 75% to 90%. In contrast, children with what’s called “high risk medulloblastoma” have five-year survival rates of 50% to 75%. Other factors — such as a child’s age and whether the tumor has spread — help determine the risk category. For this study, the researchers focused on patients with average risk medulloblastoma.
The findings appear online in the Journal of Clinical Oncology.
“Medulloblastoma is a devastating disease,” said first and corresponding author Jeff M. Michalski, MD, the Carlos A. Perez Distinguished Professor of Radiation Oncology at Washington University. “It is a malignant brain tumor that develops in the cerebellum, the back lower part of the brain that is important for coordinating movement, speech and balance. The radiation treatment for this tumor also can be challenging, especially in younger children whose brains are actively developing in these areas. There’s a balance between effectively treating the tumor without damaging children’s abilities to move, think and learn.”
He warned, “We saw higher rates of recurrence and tumor spreading in the younger patients receiving the lower dose of craniospinal radiation. In general, it’s not safe to lower the dose of radiation in children with medulloblastoma even if we know the lower dose might spare their cognitive function. However, a specific subgroup of patients — those with mutations in a gene called WNT — did well on the lower dose, so we’re now doing studies just with these specific patients to see if we can safely lower the radiation dose for them.”
