Targeted Medicines for Pediatric Low-Grade Glioma: What Families Should Know About MAPK Inhibitor Therapy

Table of Contents

• Key Points
• Understanding Pediatric Low-Grade Glioma (pLGG)
• Current Standard Therapy: Surgery, Chemotherapy, and Radiation
• What Are MAPK Inhibitors?
• The Drugs at a Glance: Doses and Results
• Managing Side Effects of MAPK Inhibitors
• How Doctors Monitor Tumor Response
• What This Means for Patients and Families
• Limitations: What We Still Don't Know
• Recommendations for Patients and Caregivers
• Frequently Asked Questions
• Source Information

Key Points

• Pediatric low-grade glioma is the most common childhood brain tumor; about 70% are driven by the MAPK pathway.
• BRAF inhibitors are used only for BRAF V600E-mutant tumors, not fusions, where they may cause paradoxical growth.
• Dabrafenib plus trametinib improved progression-free survival versus chemotherapy in BRAF V600E-mutant low-grade glioma.
• MEK inhibitors like selumetinib and trametinib are oral options, often used off-label as second-line therapy.
• Side effects include skin toxicity, heart and eye effects; growth arrest is specific to tovorafenib and reversible.

Understanding Pediatric Low-Grade Glioma (pLGG)

Pediatric low-grade gliomas are the most common brain tumors in children. They make up 30–40% of all pediatric central nervous system tumors, meaning 3 to 4 of every 10 childhood CNS tumors are pLGG.

"Low-grade" means these tumors grow slowly, but they still cause serious problems depending on where they sit in the brain. The term pLGG actually covers many different tumor types. Each type has its own look under the microscope and its own genetic fingerprint.

The 2021 World Health Organization (WHO) classification system groups these tumors into three categories:

• Pediatric-type diffuse low-grade gliomas
• Circumscribed astrocytic gliomas
• Glioneuronal and neuronal tumors

The most common single type is pilocytic astrocytoma (PA). It accounts for 10–15% of all brain tumors in children and about 5% of brain tumors in adults.

Nearly 70% of pLGGs share a common biological driver. They carry mutations in one genetic pathway, the RAS-RAF-MAPK pathway (a chain of proteins inside cells that controls growth and division). Because of this, researchers often call pLGG a "single pathway disease."

Location often matches the genetic driver. For example, pleomorphic xanthoastrocytomas usually form in the supratentorial area (upper part of the brain) and carry a specific mutation called BRAF V600E. Meanwhile, pilocytic astrocytomas more often carry BRAF fusions (where the BRAF gene joins with another gene) and grow in the posterior fossa (back of the brain) or along the optic pathway (the visual nerves).

pLGG also commonly occurs in children with neurofibromatosis type 1 (NF1), a genetic condition that raises tumor risk. Optic pathway gliomas occur in 15–20% of NF1 patients. Children with NF1 also face a higher risk of other RAS-pathway tumors, including plexiform neurofibromas (nerve-sheath tumors), brainstem gliomas, and diffuse astrocytomas.

Current Standard Therapy: Surgery, Chemotherapy, and Radiation

Surgery is the first-line treatment for symptomatic pLGG when possible. However, more than half of these tumors — over 50% — are located where surgery is not safe or feasible. These include tumors in the diencephalon (deep brain structures), brainstem, optic pathway, or spinal cord. In those cases, surgery may be limited to a biopsy or partial removal, or it may not be offered at all.

For inoperable tumors, treatment choice depends on symptoms. Tumors in the optic pathway or brainstem often need urgent therapy to preserve vision or relieve neurological symptoms.

Chemotherapy remains standard of care for inoperable or residual pLGG. It works well and is tolerated by children of all ages, including the very young. The two most common regimens are carboplatin plus vincristine or single-agent vinblastine.

Outcomes with chemotherapy are good but imperfect:

• 5-year overall survival (OS) — the chance of being alive 5 years after diagnosis — is 86–94% in recent studies.
• 5-year progression-free survival (PFS) — the chance the tumor has not grown 5 years later — is less favorable at 42–45%.
• Children with NF1 do somewhat better, with 5-year PFS of 69–85%.

Chemotherapy side effects include suppression of blood cell production (myelosuppression), gastrointestinal problems, and peripheral nerve damage affecting sensation and movement (peripheral sensory and motor neuropathy). These effects are generally manageable. However, allergic reactions to carboplatin occur in up to 8–20% of patients receiving carboplatin plus vincristine.

Radiation therapy is very effective against pLGG. In the HIT-LGG-1996 trial, radiation achieved better 10-year progression-free survival than conventional chemotherapy (62% versus 42%). Yet doctors largely avoid radiation in sporadic pLGG, and almost always avoid it in NF1-associated pLGG. The reason is the risk of serious late effects, including:

• Secondary (new) malignancies
• Neurocognitive impairment
• Hormonal dysfunction
• Growth delay
• Vasculopathy and cerebrovascular injury (blood vessel damage in the brain)

Regardless of which upfront therapy is used, unresectable pLGG recurs in nearly 50% of patients after first-line treatment. Many children need episodic treatment throughout childhood and adolescence during periods of disease progression.

Experts now view multiply recurrent pLGG like a chronic condition. The approach focuses on periodic flare-ups and symptoms. Overall survival stays excellent despite the less favorable PFS. The current goal of research is to find agents that produce durable responses and reduce the burden of treatment.

MAPK inhibitors — targeted drugs that block RAF and MEK proteins — may fill that need.

What Are MAPK Inhibitors?

Mutations in the BRAF oncogene (a gene that helps control cell growth) are among the most common genetic changes found in cancer. These changes keep the BRAF protein permanently switched on. That drives downstream signaling through MEK and ERK proteins, pushing tumor growth and proliferation.

BRAF can be altered in two main ways:

• BRAF V600E mutations: A single "hotspot" change (Val600Glu) makes the BRAF protein act as a lone monomer to drive ERK signaling.
• BRAF fusions: The BRAF gene rearranges and pairs with a fusion partner. The rearranged protein forms a dimer (a two-part complex) that keeps signaling active on its own, independent of normal RAS control.

Among the fusions, KIAA1549::BRAF is the most common. It appears in 70–80% of pilocytic astrocytomas and in 30–40% of all pLGGs. New drugs that target this widespread fusion are highly sought after.

BRAF inhibitors (like vemurafenib and dabrafenib) were among the first targeted agents tested in pLGG. They showed remarkable success in BRAF V600E-altered tumors. But surprisingly, tumors with KIAA1549::BRAF fusions grew paradoxically when treated with these drugs — a biological phenomenon now well understood at the molecular level.

Because of that risk, BRAF inhibitors are now used only in patients with BRAF V600E mutations, and they are contraindicated (not permitted) in patients with BRAF fusions.

Dabrafenib was later tested in combination with the MEK inhibitor trametinib as first-line therapy for BRAF V600E-altered low-grade glioma. The combination improved progression-free survival dramatically compared with standard chemotherapy: PFS was 20.1 months versus 7.4 months (hazard ratio, 0.31). In plain terms, patients on the targeted combination had about a two-thirds lower risk of tumor progression during the study period. The combination also had a superior safety profile.

These results changed clinical practice:

• In 2022, the FDA granted accelerated approval to the dabrafenib/trametinib combination for progressive or metastatic solid tumors with BRAF V600E mutations.
• In 2023, the FDA approved the same combination as first-line treatment for pediatric patients age 1 and older who have pLGG with a BRAF V600E mutation.

MEK inhibitors, including selumetinib, trametinib, mirdametinib, binimetinib, and cobimetinib, work one step downstream. They block MEK, the kinase protein that BRAF activates. Several have been studied in children with pLGG, with safety and efficacy data in recurrent pLGG and in NF1-associated pLGG.

Selumetinib is now being tested against standard chemotherapy in two phase 3 trials for newly diagnosed pLGG, both with and without NF1 (NCT03871257 and NCT04166409). Because selumetinib and trametinib can be prescribed off-label today, they are frequently used in the real world as second-line therapy.

The Drugs at a Glance: Doses and Results

These are the targeted agents with published phase 2 trial data in pLGG and favorable toxicity profiles. Doses are provided so families can recognize them; actual dosing is always individualized by the care team.

Dabrafenib (BRAF inhibitor)

• Dose: Children under 12 years: 2.625 mg/kg twice daily. Age 12 and older: 2.25 mg/kg twice daily. Maximum 150 mg per dose.
• Form: Oral capsule or dispersible tablet.
• Evidence: 47% overall response rate (ORR) when combined with trametinib in BRAF V600E-mutant pLGG.

Vemurafenib (BRAF inhibitor)

• Dose: 550 mg/m² twice daily (maximum 960 mg per dose).
• Form: Oral tablet.
• Evidence: Phase 1 data showed a 32% overall response rate (ORR) in BRAF V600E-mutant pLGG.

Binimetinib (MEK1/2 inhibitor)

• Dose: 32 mg/m² twice daily (maximum 45 mg per dose).
• Form: Oral tablet.
• Evidence: 43% partial response rate in NF1-related tumors; 50% partial response in pLGG with BRAF fusions; 69% in sporadic pLGG without BRAF alterations.

Cobimetinib (MEK1/2 inhibitor)

• Dose: 0.8 mg/kg tablet or 1.0 mg/kg suspension daily on a 3-weeks-on, 1-week-off schedule (maximum 60 mg per dose).
• Form: Oral tablet or suspension.
• Evidence: Phase 1/2 data showed 5% partial response and 59% stable disease.

Mirdametinib (MEK1/2 inhibitor)

• Dose: 2 mg/m² twice daily, 3 weeks on and 1 week off (maximum 4 mg per dose).
• Form: Oral capsule or dispersible tablet. It penetrates the brain well.
• Evidence: 52% ORR in plexiform neurofibroma (phase 2b); 63% ORR in pLGG (phase 1/2). So far, 12 of 19 patients (63%) achieved objective responses — 1 major, 6 partial, and 5 minor. The phase 2 portion is ongoing, including newly diagnosed patients and those with prior MEK inhibitor exposure (NCT04923126).

Selumetinib (MEK1/2 inhibitor)

• Dose: 25 mg/m² twice daily (maximum 50 mg per dose).
• Form: Oral capsule.
• Evidence: In a phase 1 trial of children with recurrent pLGG, 20% had sustained partial response. In a phase 2 trial, 36–40% achieved sustained partial response. Two-year PFS was 70% in BRAF-altered, non-NF1 pLGG and 96% in children with germline NF1.
• In NF1-associated plexiform neurofibromas, response rates were around 70%, and the FDA approved selumetinib for that indication.

Trametinib (MEK1/2 inhibitor)

• Dose: Under 6 years: 0.032 mg/kg daily. Age 6 and older: 0.025 mg/kg daily. Maximum 2 mg per dose.
• Form: Oral tablet or suspension.
• Evidence: 61% ORR in plexiform neurofibroma; 47% ORR when combined with dabrafenib in BRAF V600E-mutant pLGG. Retrospective studies support single-agent activity. Interim phase 2 results in pLGG showed roughly 47% overall response rate (complete, partial, or minor response), and a 60% response rate by volumetric assessment in NF1-associated plexiform neurofibroma.
• Approval context: FDA-approved in 2013 for adult BRAF V600E melanoma; used commonly off-label in children as molecularly guided therapy. A large prospective trial is ongoing (NCT03363217).

Tovorafenib (Type II RAF inhibitor)

• Dose: 380 mg/m² taken orally once weekly.
• Form: Oral tablet or suspension. It targets both mutant and normal (wild-type) A-Raf, B-Raf, and C-Raf proteins and can block RAF dimers, meaning it works against BRAF fusions.
• Evidence: Among 137 patients with BRAF-altered relapsed or refractory pLGG, the ORR was 51% by RAPNO criteria and 67% by RANO-HGG criteria (the primary endpoint). Twelve patients (17%) had complete responses. The median duration of response was 13.8 months.
• These patients were heavily pretreated: they entered the trial after a median of three prior lines of therapy, and 61% had already received a MEK and/or BRAF inhibitor.
• The FDA granted tovorafenib accelerated approval for recurrent or refractory pLGG in 2024. It is now being compared with standard chemotherapy (single-agent vinblastine or carboplatin/vincristine) in newly diagnosed RAF-altered pLGG.

Managing Side Effects of MAPK Inhibitors

MAPK inhibitor side effects in children are now well described. The most common treatment-related effects involve the skin, gastrointestinal system, eyes, and heart.

Skin toxicity is the most frequent issue. Rashes can be eczematous (dry, itchy, flaky) or acneiform (acne-like). Patients may also develop paronychia (painful inflammation around the fingernails or toenails) and hair color changes. Some patients develop wound complications.

Consensus guidelines from groups including a Children's Tumor Foundation advisory board recommend prevention strategies:

• Apply moisturizers and emollients regularly to maintain a healthy skin barrier.
• Use sun protection.
• Take bleach baths to reduce skin bacteria, prevent infectious complications, and ease itching.
• For adolescent patients, topical antibiotics and low-dose topical steroids help prevent facial acne in the "T zone" (forehead, nose, and chin).

Once a rash appears, treatments include topical steroids, topical and oral antibiotics, and sometimes pausing the drug until the rash resolves or improves significantly.

Mild paronychia can be managed with frequent antiseptic soaks using chlorhexidine, plus topical antibiotics and topical steroids. Dermatology specialty care is recommended for severe or persistent cases.

Wound healing problems are less common but can be serious. Children who have surgery while on therapy — for example, placement of a ventricular shunt catheter or a central venous line — may heal more slowly. Pressure sores and skin ulcerations may also take longer to heal and require wound care expertise.

Heart effects are uncommon but monitored carefully. Published reports show low rates of cardiac toxicity in children. Still, most guidelines recommend routine echocardiograms (ECHO, an ultrasound of the heart) to check for an asymptomatic drop in ejection fraction (EF) — the heart's pumping strength.

In selumetinib trials, an EF decrease greater than 10% below the normal range occurred in one pediatric patient with NF1-associated pLGG and in 20 patients (40%) with non-NF1 associated pLGG. Most cases were found on routine screening without symptoms.

Consensus recommendations for an asymptomatic EF drop beyond 10% of baseline:

1. Hold (pause) the MEK inhibitor.
2. If the EF does not improve within 4 weeks off therapy, discontinue the drug altogether.
3. EF decrease is generally reversible after stopping or pausing the medication.

Routine ECHO monitoring is recommended after 1 month of therapy, then at regular intervals (for example, every 3–6 months). Notably, tovorafenib has not been linked to cardiac side effects.

Eye problems are rarely reported in children on published MAPK inhibitor studies. In adults, however, they can cause serious vision problems and even blindness. A class effect called MEK inhibitor-associated retinopathy (MEKAR) affects anywhere from 5–90% of adult patients treated with MEK or BRAF inhibitors, depending on the report.

Symptoms include blurry vision, floaters, and sensitivity to light (photophobia). In the most severe cases, retinal detachment or retinal vein occlusion can occur. In children, MEKAR is usually self-limited and may resolve whether or not the drug is stopped.

Because visual symptoms are usually noticeable, monitoring can be done clinically. However, most practitioners still recommend an ophthalmology (eye) exam early in therapy — usually after 1 month — and then every 3–6 months. The exam should include:

• Visual acuity testing (the standard eye chart) at minimum
• Visual field testing for patients with optic pathway gliomas
• Consideration of optical coherence tomography (OCT) to detect small retinal detachments

Again, tovorafenib has not been associated with retinal or eye-related side effects.

Growth arrest is a distinctive side effect of tovorafenib. It has not been reported with the MEK inhibitors, and researchers do not yet know if it is a class effect of RAF inhibitors generally. Preliminary data show that children and adolescents stop growing while on tovorafenib, without advancement of bone age or premature closure of growth plates. This effect reverses once the drug is stopped. In fact, some patients resumed expected annual growth after therapy, and some even exceeded the expected average for their age after treatment.

Long-term toxicity data are still immature. The drugs have not been commercially available long enough to know their late effects, which is a disadvantage compared with chemotherapy. However, off-therapy data are now being collected. Researchers are tracking organ function — especially heart and eye function — plus effects on growth, puberty, vision, and neurocognitive (thinking and learning) outcomes.

How Doctors Monitor Tumor Response

The way doctors measure whether a pLGG is responding to MAPK inhibitor therapy has evolved. Early trials measured only the enhancing (bright) parts of the tumor on T1 post-contrast MRI scans. That approach was later changed, because enhancement patterns in pLGG can increase or decrease on their own without any treatment, do not reliably match true tumor volume, and do not predict outcome.

Instead, modern trials measure tumor size on T2/FLAIR MRI sequences using two-dimensional measurements. These better capture the true extent of a low-grade glioma.

The phase 2 tovorafenib trial used the Response Assessment in Neuro-Oncology High-Grade Glioma (RANO-HGG) criteria as its primary endpoint, because those were the only criteria the FDA considered validated when the trial began. Secondary response assessments used the RAPNO criteria (Response Assessment in Pediatric Neuro-Oncology Low-Grade Glioma) and the RANO-LGG criteria — both of which were designed to avoid relying on enhancement changes.

The practical message for families: a "stable" or "responding" scan may look different depending on which criteria the radiology team applies, and lack of contrast enhancement does not mean the tumor is gone. Serial MRIs remain the backbone of monitoring.

What This Means for Patients and Families

MAPK inhibitors bring practical advantages beyond their effectiveness. They are oral medications, and most — except selumetinib — come as a liquid formulation or dispersible tablet. That makes them ideal for young children and for patients who need feeding tubes (enteral nutrition).

Dosing schedules are convenient:

• MEK and BRAF inhibitors are given once or twice daily, based on pharmacokinetic (drug absorption) studies.
• Some MEK inhibitors require an empty stomach for the drug to absorb properly.
• Tovorafenib is unique: it is taken just once weekly, with or without food.

Oral therapy can reduce the burden of clinic visits. Unlike weekly intravenous chemotherapy, MAPK inhibitors need fewer ambulatory visits for administration.

This matters most for children living in low-resource or geographically isolated areas. Ongoing studies are exploring whether MAPK inhibitors make sense as front-line therapy in limited populations, because the oral format may reduce "financial toxicity" — the cost and logistical strain of treatment — for families in low- and middle-income countries (LMIC).

The authors note that while Phase 3 trials are designed to answer which front-line therapy is safest and most effective, the use of MAPK inhibitors in the front-line setting is already being discussed for limited-resource populations.

Limitations: What We Still Don't Know

This review is based on the evidence available in early 2025, and important gaps remain.

• Long-term side effects are unknown. MAPK inhibitors have not been on the market long enough to define late effects, unlike decades of chemotherapy experience.
• Some evidence is retrospective. Trametinib monotherapy, for example, is supported mainly by retrospective analyses while larger prospective trials continue.
• Front-line phase 3 results are still pending. Trials comparing selumetinib with standard chemotherapy in newly diagnosed patients (NCT03871257 and NCT04166409) are ongoing, as is the trametinib trial (NCT03363217) and the mirdametinib study (NCT04923126).
• The growth-arrest effect of tovorafenib may or may not be unique. Whether it is a class effect of other RAF inhibitors is unknown.
• Off-label use carries uncertainty. Selumetinib and trametinib are prescribed off-label for pLGG while trials finish. Off-label use lacks the formal pediatric labeling, dosing refinements, and long-term safety surveillance that approval brings.
• The review was authored by specialists at major U.S. children's hospitals, and their perspective reflects high-resource settings, though they explicitly address limited-resource environments.

Recommendations for Patients and Caregivers

If your child has a low-grade glioma, here is what this review suggests you discuss with your care team.

1. Ask about molecular testing. Knowing whether the tumor has a BRAF V600E mutation, a BRAF fusion like KIAA1549::BRAF, or an NF1 association directly determines which targeted drug is safe. BRAF inhibitors must be avoided in fusion-driven tumors.
2. Ask whether a MAPK inhibitor is an option. For children who have relapsed after chemotherapy, MEK and RAF inhibitors are now established second-line (or later) options with meaningful response rates.
3. Ask about clinical trials. Front-line phase 3 trials are actively enrolling children with newly diagnosed pLGG. Trial participation may offer access to new agents like tovorafenib before they become widely available.
4. Start skin care early. Moisturizers, sun protection, and bleach baths can prevent the most common side effects. Ask for a dermatology referral early if a rash or paronychia develops.
5. Keep scheduled heart and eye checks. Expect an ECHO after about 1 month of therapy and then every 3–6 months. Expect an ophthalmology exam on a similar schedule, especially for optic pathway tumors.
6. Watch growth carefully on tovorafenib. Growth arrest appears reversible after stopping the drug, but height and bone age should be tracked.
7. Do not stop a drug without medical guidance. Ruff some side effects, pausing the drug is the right move — for example, a significant EF drop. But the decision to hold, resume, or stop must be made with the oncology team.
8. Ask about practical access support. Oral, once-weekly options like tovorafenib reduce clinic visits. If travel, cost, or geography is a barrier, ask your team about patient assistance programs and telehealth options.

Frequently Asked Questions

Why is the BRAF V600E mutation status of my child's tumor important before starting a MAPK inhibitor?

Knowing the genetic driver decides which targeted drug is safe. BRAF inhibitors like dabrafenib or vemurafenib work only for BRAF V600E-mutant tumors. In tumors with BRAF fusions, these drugs caused paradoxical tumor growth and are not permitted. MEK inhibitors, however, may still be an option for fusion-driven tumors. Ask your care team about molecular testing.

What are the common side effects of MEK inhibitors in children?

Common side effects include skin rashes, dryness, paronychia around nails, hair color changes, and sometimes wound healing problems. Heart effects are uncommon, but doctors monitor heart function with echocardiograms. Eye problems are rarely reported in children, though routine eye exams are often recommended. Growth arrest has been reported only with tovorafenib, not MEK inhibitors.

My child has a low-grade glioma with a BRAF V600E mutation. What treatment options are available?

For BRAF V600E-altered low-grade glioma, the combination of dabrafenib plus trametinib improved progression-free survival significantly compared with standard chemotherapy in a clinical trial. In 2023, this combination was approved as first-line treatment for children aged 1 and older with this specific mutation. BRAF inhibitors are not used for fusion-driven tumors.

What does 'progression-free survival' mean for my child's tumor response?

Progression-free survival is the length of time after treatment that the tumor does not grow or progress. For example, in one study of BRAF V600E-mutant low-grade glioma, patients receiving dabrafenib plus trametinib had a median progression-free survival of 20.1 months versus 7.4 months with standard chemotherapy.

How will doctors know if the MAPK inhibitor is working?

Doctors use serial MRI scans to monitor tumor response. Modern criteria measure tumor size on T2/FLAIR sequences rather than relying only on contrast enhancement, because enhancement patterns can change without treatment. Stable or responding scans may look different depending on the criteria used. Your care team will interpret scans alongside your child's symptoms.

My child has NF1 and a low-grade glioma. Is a MAPK inhibitor an option?

Yes. Selumetinib, a MEK inhibitor, has shown response rates in children with NF1-associated low-grade glioma. In a phase 2 trial, sustained partial responses occurred in 36–40% of patients, and two-year progression-free survival was 96% in children with germline NF1. Selumetinib is also approved for NF1-related plexiform neurofibromas.

What is unique about tovorafenib compared with other MAPK inhibitors?

Tovorafenib is a type II RAF inhibitor taken orally once weekly. It can block RAF dimers, making it effective against BRAF fusions. In a study of heavily pretreated relapsed or refractory low-grade glioma, overall response rate was 51% by RAPNO criteria. It is associated with reversible growth arrest in children.

My child has a low-grade glioma and we were offered a MAPK inhibitor. Should we get a second opinion before starting?

A second opinion is worthwhile because the safe choice of targeted therapy depends on the tumor's exact genetic driver. BRAF inhibitors must not be used in tumors with BRAF fusions, while they are effective in BRAF V600E-mutant tumors. MEK inhibitors and newer RAF inhibitors are options for relapsed disease. A second opinion can confirm the molecular testing, review whether first-line chemotherapy is still preferred, and identify relevant clinical trials. Talk to your care team about sending pathology and MRI reports. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

Original article title: Integrating MAPK pathway inhibition into standard-of-care therapy for pediatric low-grade glioma.

Authors: Crotty EE, Sato AA, Abdelbaki MS.

Publication details: Published in Frontiers in Oncology, Volume 15, article 1520316. Received October 31, 2024; accepted January 22, 2025; published February 11, 2025. DOI: 10.3389/fonc.2025.1520316.

This patient-friendly article is based on peer-reviewed research. It is intended for educational purposes and does not replace individualized medical advice from your child's oncology team.