Retevmo Approval the Beginning of Targeted Therapy for RET-Mutant Childhood Cancer

The recent Food and Drug Administration (FDA) approval of Retevmo (selpercatinib) for children aged 2 years and older with RET-mutant positive cancers marks the start of more targeted therapies for this patient population, according to an expert.

“The approval is the beginning of us trying to understand the best way of using these targeted drugs. It may well be that there are other ways that we can use them in the future,” Dr. Daniel Morgenstern said in an interview with CURE®.

Morgenstern is a pediatric oncologist at the University of Toronto’s Hospital for Sick Children. In a recent interview, he discussed the May 2024 approval of Retevmo for RET-positive pediatric cancers.

Where Retevmo Fits in With Standard Therapies

The drug was approved for patients with advanced or metastatic medullary thyroid cancer with a RET mutation; advanced or metastatic thyroid cancer with a RET gene fusion that requires systemic therapy and is not responsive to radioactive iodine; and locally advanced or metastatic solid tumors that progressed on or after systemic therapy and have a RET gene fusion and no other satisfactory alternative treatments.

According to Morgenstern, most pediatric RET-mutant diseases are thyroid cancers, which are typically treated with the surgical removal of the thyroid. Then, depending on where the disease spreads — and it commonly spreads to the lungs — radioactive iodine is typically used as the standard of care. According to the American Cancer Society, iodine is attracted to thyroid cells, even if they have moved to different parts of the body. Once the iodine binds to the cancer, the radiotherapy then kills the cancer cells.

“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,” Morgenstern said.

Morgenstern did mention, however, that there is ongoing research analyzing whether Retevmo makes radioactive iodine more effective in treating cancer. As such, determining when the best time to give the drug remains an unanswered question.

“One of the questions is: could we be using these targeted drugs earlier? It might be effective earlier in combination with radioactive iodine, for instance,” Morgenstern said. “And the other question is, if we’re using this drug and patients respond — and we have some excellent responses — how long do we carry on the drug, and what happens if we stop it and the disease starts to recur?”

What Patients and Caregivers Can Expect With Retevmo Treatment

Retevmo is administered orally. Regarding side effects, Morgenstern said that the drug is well-tolerated.

“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.”

In the trial that led to the drug’s FDA approval on May 29, the most common side effects were musculoskeletal pain, diarrhea, headache, nausea, vomiting, COVID-19 infection, abdominal pain, fatigue, fever and hemorrhage (bleeding). Severe laboratory abnormalities (changes in blood tests) occurred in 5% of patients.

While Retevmo is effective and well-tolerated, there is still far more work that needs to be done in the pediatric cancer space, Morgenstern said.

“There is, in pediatric oncology, still a desperate need for us to find equivalent targets to RET in other childhood cancers and to develop drugs for those targets. One of the challenges we have in pediatric cancer is that generally, drugs still get developed for adult indications first and foremost,” he said. “And the reason there is a drug for this setting is not because a company went out and developed a drug for pediatric thyroid cancer, it's because RET is a relevant target in adult cancers, and there was a market and a need and justification to develop a drug for that.”

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