Childhood cancers: brain cancer

These are the most common childhood tumors

Brain tumors can be located in the posterior fossa of the skull, where the cerebellum – the organ that regulates balance – is located, or in the cerebral hemispheres. There are generally three main types of brain tumor.

• Glial tumors, which are the most common: these develop in the support tissues (glial cells) of the encephalon or the spinal cord. This term covers several types of tumor, with variable aggressiveness. These tumors are very different from gliomas occurring in adults.
• Embryonal tumors, which include medulloblastoma, located in the cerebellum, and atypical teratoid/rhabdoid tumors (AT/RT).
• Ependymomas, which originate in the ependyma, the lining of the ventricular system and the center of the spinal cord, and are relatively rare.

The symptoms that suggest a brain tumor most frequently arise due to the pressure the tumor puts on the skull. They also depend on its precise location: headaches, nausea, vomiting, vision changes, balance problems and behavioral changes are all signs that could indicate a mass in the brain.

These symptoms are not sufficient to make a diagnosis; only an imaging exam or even a biopsy will allow a precise diagnosis and determination of the nature of the tumor, its location and its degree of aggressiveness. Once these parameters have been determined, the terms of the treatments may then be established. These represent surgery, radiotherapy, proton therapy, chemotherapy and targeted therapies. Most of the time, a combination of these treatments will be offered.

Better understanding the various forms of brain tumor. Brain tumors cover a wide variety of pathologies that can be considered rare. Two types of brain tumor are being studied in particular at Institut Curie: rhabdoid tumors and medulloblastomas.

Medulloblastomas are the most common brain tumors in children. The annual occurrence of medulloblastomas is one per 20,000 children. The latest findings have helped improve recovery, which has now reached close to 70%. medulloblastomas develop in the cerebellum, most frequently in the vermis. They are malignant tumors whose tissue resembles embryonic tissue. They are invasive, and can metastasize throughout the entire central nervous system via the cerebrospinal fluid. At the time of diagnosis, almost half of children present metastases, which are rarely symptomatic.

At Institut Curie, new proton therapy techniques, which involve intensity modulation and pencil beam scanning (PBS), help improve treatment of young patients suffering from medulloblastoma. The location of this tumor in the cerebellum, at the rear of the brain, requires targeted therapies to spare the brain, a challenge which is perfectly suited to proton therapy treatment. Olivier Ayrault’s team is studying the development mechanisms of medulloblastomas and, in particular, the specificities of one of the four sub-groups identified to date. The goal in the long term is to come up with new therapeutic leads.

Atypical teratoid and rhabdoid tumors are rare, with one case per million each year. These tumors are extremely aggressive and the prognosis remains very poor: around 25% overall survival after two years.  

Atypical teratoid and rhabdoid tumors (AT/RT) are due to the extinction of a tumor-suppressing gene known as SMARCB1 or INI1, discovered in 1998 by the laboratory of Olivier Delattre. Some of the consequences of this extinction provide indicators for targeted treatment of rhabdoid tumors. 

Franck Bourdeaut is the national principal investigator of a clinical trial in partnership with the Boston-based company EpiZyme, which has synthesized a molecule capable of offsetting the loss of the SMARCB1 function. Since these tumors are extremely aggressive and grow fast, both locally and as metastases, the results of this test are eagerly anticipated.