The U.S. Food and Drug Administration (FDA) has approved Ayvakit (avapritinib) for treating adults with unresectable or metastatic gastrointestinal stromal tumor (GIST) with a platelet-derived growth factor receptor alpha (PDGFRA) exon 18 mutation.

The approval was largely based on a phase I study involving 43 adults with GIST who had a PDGFRA exon 18 mutation (including 38 patients with the more specific PDGFRA D842V mutation). The study showed an overall response rate of 84% ( 7% with a complete tumor shrinkage and 77% with a partial tumor shrinkage).

Common side effects include edema, nausea, fatigue/asthenia, cognitive impairment, vomiting, decreased appetite, diarrhea, hair color changes, increased lacrimation, abdominal pain, constipation, rash and dizziness. The drug can cause intracranial hemorrhage as well as central nervous system effects (cognitive impairment, dizziness, sleep disorders, mood disorders, speech disorders and hallucinations). If these latter symptoms appear, the drug should be discontinued, or the dosage reduced, depending on the severity. The recommended dose is 300 mg once daily, taken as an oral tablet(s).

GIST a rare sarcoma that occurs in the gastrointestinal tract, usually in the stomach or small intestine. Approximately 10% of  GISTs harbor a PDGFRA exon 18 mutation and historically, these tumors do not respond well to treatment.

In a news release, Richard Pazdur, MD, director of the FDA’s Oncology Center of Excellence  said,  “GIST harboring a PDGFRA exon 18 mutation do not respond to standard therapies for GIST. However, today’s approval provides patients with the first drug specifically approved for GIST harboring this mutation,” adding, “Clinical trials showed a high response rate with almost 85% of patients experiencing tumor shrinkage with this targeted drug.”

The FDA is also advising that avapritinib can cause harm to a developing fetus or newborn baby and that effective contraception should be used by adults of reproductive age during treatment with the drug, and for six weeks after the final dose of avapritinib.

Avapritinib is a kinase inhibitor developed by Blueprint Medicines Corporation. The FDA granted this application a Breakthrough Therapy designation, a Fast Track designation, and an Orphan Drug designation, to further underline the important unmet need this drug will address.

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