Childhood brain tumour is really two cancers

The most common type of malignant childhood brain tumour is actually two different types of cancer, researchers said in a study they said also suggested the youngest patients could receive less toxic treatments.

The cancer, called medulloblastoma, is usually curable but children can suffer lifetime effects from treatment, which can include surgery, chemotherapy and radiation.

Tests in mice show there are two distinct forms of the cancer and one might require less treatment, Dr Richard Gilbertson of St Jude Children's Research Hospital in Memphis, Tennessee, and an international team of colleagues found.

Distinct subtypes of this cancer

"Ten years ago, medulloblastoma was regarded as a single disease, and all children with this brain tumour got the same treatment. This study shows clearly that there are distinct subtypes of this cancer that come from uniquely susceptible cell types in the brain that acquire specific mutations," Gilbertson said.

The findings "have profound implications for future research and treatment of this important childhood cancer," they wrote in their report in the journal Nature.

More complicated than originally thought

The study adds to a growing body of research demonstrating that cancer is far more complicated than doctors thought. Cancer was once diagnosed and treated based on where in the body it started.

But more and more evidence suggests that using the organ of origin to diagnose and treat cancer only works sometimes and it may be more important to genetically "type" a tumour.

The researchers had already found two distinct genetic activities in medulloblastoma tumors - one developed via a genetic pathway called "wingless," or WNT, and the other via a gene nicknamed "sonic hedgehog," or SHH. Mutations in these genes account for about 40% of the estimated 400 medulloblastoma tumours diagnosed annually in US children.

The SHH type of tumour most commonly affects very young children, who have an 80% survival rate.

"WNT-subtype medulloblastomas are strikingly different. Arising in much older children, these highly curable tumours have 'classic' morphology," the researchers added.

They genetically engineered mice that often developed these tumours after they were born and studied them. The different tumour types started at slightly different places and involved different cells.

This could be good news for younger medulloblastoma patients, who might be cured with gentler regimens, although the researchers said further study will be needed to confirm what treatment is best.

(Reuters Health, December 2010)