FDA Approves Retevmo for RET-Positive Pediatric Cancers

The Food and Drug Administration (FDA) granted an accelerated approval to Retevmo (selpercatinib) for the children aged two and older with one of the following diseases:

• Advanced or metastatic medullary thyroid cancer with a RET mutation
• Advanced or metastatic thyroid cancer with a RET gene fusion who need systemic therapy and whose disease did not respond to radioactive iodine
• Locally advanced or metastatic solid tumors with a RET gene fusion that progressed on or after prior systemic therapy and/or have no other satisfactory alternative treatment options

Of note, this is the first targeted drug to be FDA approved for patients under the age of 12 who have RET alterations. The agent was approved in 2020 for certain patients over the age of 12.

The approval is based off findings from the LIBRETTO-121 clinical trial, which investigated oral Retevmo in 25 patients between the ages of 2 to 20 with locally advanced or metastatic RET-activated solid tumors that are non-responsive to therapies or have no standard systemic curative therapies available.

The main goals of the trial were overall response rate (ORR; percentage of patients whose disease shrinks or disappears from treatment) and duration of response (DOR; how long patients live without complications from the cancer).

Confirmed ORR was 48%, and the median DOR was not yet reached, meaning that not enough patients experienced a disease-related event for the researchers to calculate the average time to event. Notably, 92% of patients were still responding to treatment at 12 months.

Among the 14 patients with RET-mutant medullary thyroid cancer who experienced a durable response, the ORR was 43%. For the 10 patients with RET fusion-positive thyroid cancer who experienced a durable response, the ORR was 60%.

The most common side effects that occurred in 25% or more of patients were: musculoskeletal pain, diarrhea, headache, nausea, vomiting, coronavirus infection, abdominal pain, fatigue, fever and hemorrhage. The most common moderate to severe (grade 3 or 4) laboratory abnormalities, which occurred in 5% of patients were decreased calcium, decreased hemoglobin and decreased neutrophils (a type of white blood cell).

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