FDA Approval: Selumetinib (Koselugo) for Childhood Cancer

The tumors this drug treats are not cancer

This is the first thing to be clear about. On April 10, 2020, the FDA approved selumetinib, sold as Koselugo. The approved use was for children aged 2 and over with neurofibromatosis type 1 who have symptomatic, inoperable plexiform neurofibromas.

Plexiform neurofibromas are benign. They are not malignant, and they do not spread the way cancer does. But the word benign can be misleading here. These tumors grow along nerves, they tangle through healthy tissue, and they can cause real harm.

The drug is handled by pediatric oncology teams, and the story sits inside cancer medicine for good reasons. Here is why.

What neurofibromatosis type 1 does

NF1 is a genetic condition. MedlinePlus describes its hallmarks: flat brown patches on the skin called cafe-au-lait spots, freckling in the armpits and groin, and tumors that grow along nerves.

Most of those tumors are neurofibromas, and most are benign. A plexiform neurofibroma is a larger, deeper version that spreads along a nerve and its branches. In the trial that supported approval, the problems these tumors caused included disfigurement, trouble moving, pain, breathing problems, vision problems, and bladder or bowel trouble.

Surgery is the traditional answer. It often is not possible. The tumor may wrap around nerves and blood vessels so closely that cutting it out would cause more damage than the tumor does. That is what the word inoperable in the label means.

Where cancer risk enters the picture

People with NF1 do carry a raised risk of certain cancers. NCI reports that about 4% of people with NF1 develop a malignant peripheral nerve sheath tumor. That is a cancer that starts in the lining of a nerve, and it usually appears after many years.

MedlinePlus adds that NF1 also raises the risk of brain tumors, including optic gliomas that grow along the nerve to the eye, and of leukemia. Our overview of childhood cancer covers how those diagnoses are worked up.

So a child with NF1 is often followed by a cancer center. The plexiform neurofibroma itself, though, is not cancer.

How the drug works

Selumetinib blocks an enzyme called MEK. MEK sits on a signaling chain that tells cells to grow. In NF1, the gene that normally puts a brake on that chain is faulty, so the signal runs too freely.

Blocking MEK turns the volume back down. This is a targeted therapy: it aims at a specific molecular step rather than at dividing cells in general.

The dose in the label is worked out from body surface area, taken by mouth twice a day, until the disease worsens or side effects become unacceptable.

Because that amount depends on body size, it is worked out for each child. Give the capsules exactly as the child's own specialist prescribed them.

What the evidence showed

The approval rested on a trial called SPRINT. Fifty children took selumetinib. Their median age was 10.2 years.

The main measure was overall response rate. Here that meant the tumor shrank by at least 20% in volume on MRI, confirmed on a later scan.

Thirty-three of the 50 children, or 66%, had a response. The 95% confidence interval ran from 51% to 79%, meaning the true rate in a wider group is likely somewhere in that band. None had a complete response, where the tumor disappears altogether. Responses took time: the median wait for one was 7.2 months.

The label carries warnings for heart muscle weakening, eye problems, stomach and bowel effects, skin effects, raised creatine phosphokinase, raised vitamin E, and bleeding risk.

Where the approval has gone since

The label has widened. On September 10, 2025, the FDA approved a granule form for children aged 1 and over. That change rested on showing the granules deliver similar drug levels to the capsules, not on a new efficacy trial.

When to seek advice

If NF1 runs in your family or a child has several cafe-au-lait spots, ask a pediatrician about a referral to genetics. NF1 is usually diagnosed on clinical signs in early childhood.

For a child already diagnosed, ask for prompt review if you notice any of these:

• A lump that suddenly grows faster than it has been growing.
• New or worsening pain in one spot, especially pain that wakes a child at night.
• New weakness, numbness, or loss of a skill the child had.
• Any change in vision, or a bulging eye.
• New trouble with breathing, swallowing, or passing urine or stool.

A fast change in a known neurofibroma is the signal that matters most, because that is how a malignant peripheral nerve sheath tumor tends to announce itself.

What this approval cannot tell you

• It does not cover neurofibromatosis type 2, schwannomatosis, or tumors outside the approved description.
• Two thirds of children responded. One third did not, and the response was partial in every case.
• Shrinking a tumor on MRI is the measure that was used. The trial was not built to show long-term effects on survival.
• The 2025 change was a new formulation, not new evidence of benefit.
• Trials enroll people who meet strict criteria, so results may not carry over to every child. Trial phases explains what each stage of testing can and cannot settle.

Sources

• FDA approval package for KOSELUGO (selumetinib), NDA 213756, April 10, 2020
• FDA prescribing information for KOSELUGO (selumetinib), 2020
• FDA approves selumetinib for pediatric patients 1 year of age and older with NF1
• MedlinePlus Genetics: Neurofibromatosis type 1
• NCI PDQ: Childhood Soft Tissue Sarcoma Treatment (Health Professional Version)

How this page was made

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

Cancer Explained is published by the National Cancer Information Foundation. It is not medical advice and does not suggest a test or treatment.

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