FDA Approves Retevmo for Some With Medullary Thyroid Cancer

The Food and Drug Administration (FDA) approved Retevmo (selpercatinib) for the treatment of adults and children aged 2 years and older with advanced or metastatic medullary thyroid cancer with a RET mutation who require systemic therapy.

According to the alert from the FDA, patients would have a RET mutation detected by an FDA-approved test.

This approval was based on findings from the LIBRETTO-531 trial, which assessed treatment with Retevmo in adults and adolescents with advanced or metastatic RET-mutant medullary thyroid cancer. In particular, patients were randomly assigned to receive treatment with Retevmo or physician’s choice of cabozantinib or Caprelsa (vandetanib). Patients in the Retevmo group received 160 milligrams of the drug twice per day, and those in the control group were treated with 140 mg once per day of cabozantinib or 300 mg once per day of Caprelsa.

The main area of interest for researchers conducting this trial was progression-free survival, defined as the time during and after treatment when a patient with cancer lives with the disease without worsening. The median progression-free survival was not reached in the Retevmo group compared with 16.8 months in the control group. Of note, when median progression-free survival is not reached in a trial, it means that at least half of the patients in the study have not experienced disease progression or death from any cause.

The clinical benefit of treatment with Retevmo was supported by findings from a prespecified analysis, which demonstrated that patients in the Retevmo group reported less time with severe side effect issues compared with those in the control group.

The most common side effects, occurring in at least 25% of patients in the trial, included edema (swelling), hypertension (high blood pressure), fatigue, dry mouth and diarrhea. The most common severe or life-threatening laboratory abnormalities, occurring in at least 5% of patients, included increased alanine aminotransferase levels (possibly indicating liver damage), decreased lymphocyte counts (a type of white blood cell that plays a role in the immune system), increased alkaline phosphatase levels (indicative of liver issues), decreased neutrophil counts (a type of white blood cell that helps the body fight infection), decreased calcium levels, increased blood creatinine levels (possibly indicating kidney dysfunction) and increased aspartate aminotransferase levels (a sign of heart or liver damage).

Retevmo previously received accelerated approval for this indication in patients aged 12 years and older in 2020. In May of 2024, the FDA granted accelerated approval to Retevmo for children aged 2 years and older.

After the approval this year, CURE® spoke with a pediatric oncologist to learn more about the importance of this treatment option.

“Even in the patient population of children with thyroid cancer and RET abnormalities, at least at the moment, this is not the immediate go-to drug for patients as soon as they walk in the clinic door, because there are other standard approaches such as surgery and radioactive iodine that we think patients should receive first,” said Dr. Daniel Morgenstern, pediatric oncologist at the University of Toronto’s Hospital for Sick Children.

He added that Retevmo is often well tolerated in this patient population.

“Most of the time the side effects are really pretty minimal,” he said. “Like with most medicines, it can cause tummy upset, nausea and vomiting, diarrhea — that sort of thing. But it’s pretty rare. Occasionally it can cause changes in blood tests or some rashes, but normally for our patients, it’s been remarkably well-tolerated.”

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