2024-03-01 18:00:00
In children under 15, tumors of the central nervous system are among the most common cancers (27%), just behind leukemia (28%).
Among these central nervous system tumors, brain tumors affect nearly 500 children each year. These are embryonal tumors, gliomas, ependymomas, etc.
These pediatric tumors are biologically very different from those of adults and develop in very sensitive, still developing regions.
1 case per 20,000 children
Medulloblastoma is the most common malignant brain tumor in children with 1 case per 20,000 children and a peak incidence between the ages of 2 and 8 years.
It is part of the family of embryonal tumors (which develop from primitive cells, called embryonic) and usually originates from the cerebellum, this area located under the cerebral hemispheres and behind the brain stem.
Medulloblastoma constitutes a group of very heterogeneous tumors, divided into four subgroups. These were identified based on prognosis and expressed genes. Treatments cannot exceed a survival rate of 70% to 80% at 5 years.
For some subtypes, the prognosis is even worse. Ultimately, the average survival rate for medulloblastoma is lower than the overall 5-year survival average for all pediatric cancers, of around 83%. This is due, in particular, to his aggressiveness.
An often invasive tumor
The tumor “is invasive and can metastasize throughout the central nervous system, via the cerebrospinal fluid. At the time of diagnosis, almost half of children present with metastases which are rarely symptomatic,” notes the Gustave-Roussy anticancer center (Villejuif) on its website.
Intracranial hypertension is the first sign of medulloblastoma. It is “associated with a more or less marked balance disorder. Cranial nerve palsies can occur if there is infiltration of the brainstem by the tumor. The motor pathways are generally affected later,” adds the Gustave-Roussy center. Diagnosis is based on MRI and biopsy.
Treatment includes surgery, chemotherapy and radiotherapy. While surgery is often the first step, chemotherapy is sometimes administered before removing the tumor, especially if it is metastatic. In children under 5 years old, radiotherapy, which is particularly toxic, is avoided as much as possible.
The success of the treatment will depend on the quality of the surgery (complete or not), the presence or absence of metastases, and the biological factors of the tumor.
We speak of standard risk – when all the conditions are met for the treatment to be successful. In high-risk patients, the overall survival rate drops to 30 to 60%.
A lack of targeted treatments
Despite the identification of subgroups, targeted treatments for this brain tumor are not sufficiently developed.
This is why the “Signaling, development and brain tumors” team, led by Dr Olivier Ayrault at the Curie Institute (Paris), was created. Thus, in 2018, the Signalization team was able to identify the involvement of the SRC protein in group 4 medulloblastoma, the most common.
“Studies are underway to evaluate how to target this SRC protein and develop new therapeutic strategies. This work is carried out in collaboration on an international scale (Germany, England, Canada, Japan and the United States) and in direct contact with clinical teams in France, in particular within the framework of Paris Kids Cancer supported by the AP- HP, Gustave Roussy and the Curie Institute,” specifies the Curie Institute in a press release.
Another team from the institute is working more precisely on the subtype called “group 3”, which is particularly aggressive. Again, no targeted treatment is available. After the discovery of a signaling pathway activated in these cancers, researchers identified a drug targeting this signaling pathway.
Thus, the development of targeted and more effective treatments must first require a better understanding of all the mechanisms involved in the formation of medulloblastoma cancer cells.
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