Pediatric Low-Grade Gliomas (LGG)

Pediatric Low-Grade Gliomas (LGG)

Low grade gliomas (LGG) are a group of slow-growing tumors that can occur in numerous locations throughout the brain and spinal cord. They are the most common central nervous system tumors in children and adolescents. Types of LGG include pilocytic astrocytoma, pilomyxoid astrocytoma, and ganglioglioma. Pediatric LGG rarely spread beyond their site of origin and are often referred to as benign (not cancerous) as most can be cured with surgical removal if this is feasible. However, LGG may occur in sites in the brain such as the vision tracts where surgery is not recommended. In this situation, patients often require multiple courses of therapies, including chemotherapy or radiation, to keep the tumor from growing.

Location

Pediatric LGG occur in any location in the brain or spinal cord but most commonly occur in the bottom portion of the brain known as the cerebellum.

Symptoms

Symptoms depend on the location of the tumor but may include vision changes, headaches, vomiting (most frequently in the morning), or balance issues.

Treatment

If the tumor is in a location where surgery is feasible, the curative treatment for pediatric low-grade gliomas is complete removal. Some LGG do not grow for long periods (or ever), even if a small portion remains after surgery. If a low-grade glioma is detected on imaging but does not grow over time and is not causing symptoms, patients can be observed without treatment as these tumors are not aggressive and typically do not spread.

However, for tumors in areas of the brain where surgery is not feasible (e.g., in the vision tracts where surgery would cause blindness), that grow over time or are causing symptoms, chemotherapy is most common used. There are several chemotherapy drugs and regimens that are used for LGG. These typically consist of low doses of drugs used over a long period of time. The purpose of chemotherapy in low-grade glioma is not to make the tumor disappear, but instead to prevent it from continuing to grow and cause symptoms. Radiation therapy is an extremely effective treatment for LGG, but due to its short- and long-term side effects is typically avoided until patients are at least 10 years old.

More recently, molecularly targeted drugs that work against key cancer pathways and can be taken by mouth have been developed, including drugs that target the MAPK signaling pathway such as Dabrafenib, Trametinib, and Selumetinib. The choice of which type of MAPK pathway inhibitor to take is often based on the specific molecular changes in the patient’s tumor.

Prognosis

The 10-year overall survival for pediatric LGG is over 90%, with the best survival in patients whose tumors can be completely removed with surgery. Tumors that can’t be resected often continue to grow, although this does not typically lead to death.

Incidence

LGG are the most common central nervous system tumors seen in children and adolescents, accounting for about 33% of brain and spinal cord tumors in this population.

Age Distribution

LGG can be diagnosed at any age in pediatric patients from infancy to young adults. LGG diagnosed in infants have a poorer prognosis due to their tendency to spread throughout the central nervous system.

Risk Factors

Patients with Neurofibromatosis Type 1 have a particularly high risk of developing LGG, particularly along their vision tracts; these patients should undergo regular tumor surveillance to detect these tumors early prior to the onset of vision loss. Patients with Tuberous Sclerosis Complex are at higher risk of developing a specific type of LGG known as subependymal giant cell astrocytoma. Patients with Noonan syndrome are also at higher risk of developing LGG in childhood.

Molecular Profile

All pediatric LGG are characterized by activation of the MAPK pathway. The most common genetic change seen in these tumors is a fusion (abnormal combination) of 2 genes: BRAF and KIAA1549. Other changes may include the BRAFV600E mutation or mutations or fusions of other MAPK pathway genes such as FGFR1/2, NF1, RAF1, or NTRK.

Content last reviewed:

April 2022

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