Thyroid cancer treatment has advanced as the Food and Drug Administration (FDA) grants traditional approval to selpercatinib (Retevmo, Eli Lilly) for treating adult and pediatric patients aged 2 years and older with advanced or metastatic RET fusion-positive thyroid cancer. This approval is specifically for patients who require systemic therapy and are refractory to radioactive iodine (if radioactive iodine is appropriate). Selpercatinib previously received accelerated approval for this indication in patients aged 12 years and older in 2020.
The efficacy of selpercatinib was evaluated in the LIBRETTO-001 (NCT03157128) clinical trial, which was a multicenter, open-label, multi-cohort study. The trial included 65 patients with RET fusion-positive thyroid cancer who were refractory to radioactive iodine (if it was an appropriate treatment option) and who were either systemic therapy-naïve or previously treated. The patients were divided into separate cohorts based on their treatment history.
The major efficacy outcome measures were overall response rate (ORR) and duration of response (DOR). In the 41 previously treated patients, the ORR was 85% (95% CI: 71%, 94%), while in the 24 systemic therapy-naïve patients, the ORR was 96% (95% CI: 79%, 100%). The median DOR was 26.7 months (95% CI: 12.1, not evaluable [NE]) for previously treated patients and not evaluable (NE) (95% CI: 42.8, NE) for systemic therapy-naïve patients.
Selpercatinib Shows Promising Results in Pediatric and Young Adult Thyroid Cancer Patients
Supportive evidence came from the LIBRETTO-121 (J2G-OX-JZJJ; NCT03899792) study, an international, single-arm, multi-cohort clinical trial of selpercatinib in pediatric and young adult patients with advanced RET-altered solid tumors. This study included 10 pediatric and young adult patients with RET fusion-positive thyroid cancer, showing an ORR of 60% (95% CI: 26%, 88%) and a duration of response of 12 months or more in 83% of the patients.
The most common adverse reactions observed in patients treated with selpercatinib (≥25%) were edema, diarrhea, fatigue, dry mouth, hypertension, abdominal pain, constipation, rash, nausea, and headache. The most common Grade 3 or 4 laboratory abnormalities (≥5%) included decreased lymphocytes, increased alanine aminotransferase (ALT), increased aspartate aminotransferase (AST), decreased sodium, and decreased calcium levels. The recommended dose of selpercatinib for pediatric patients aged 2 to less than 12 years is based on body surface area, while for patients aged 12 years and older, it is based on weight. Detailed dosing information can be found in the prescribing information.
This traditional approval of selpercatinib represents a significant advancement for patients with RET fusion-positive thyroid cancer, particularly those who are refractory to standard treatments such as radioactive iodine. The high ORR and substantial duration of response in both previously treated and systemic therapy-naïve patients highlight the drug’s efficacy. The supportive data from the pediatric population further underscore its potential benefits across a wide age range.
A New Hope for RET Fusion-Positive Thyroid Cancer Patients
The LIBRETTO-001 trial included 65 patients with RET fusion-positive thyroid cancer, where previously treated patients exhibited an overall response rate (ORR) of 85% and a median duration of response (DOR) of 26.7 months, while systemic therapy-naïve patients had an ORR of 96% with a non-evaluable median DOR. In the LIBRETTO-121 trial, which included 10 pediatric and young adult patients, the ORR was 60%, with 83% of the patients experiencing a duration of response of 12 months or more.
The safety profile of selpercatinib was consistent with previous findings, with common adverse reactions including edema, diarrhea, fatigue, and hypertension. Laboratory abnormalities such as decreased lymphocytes and increased liver enzymes were also noted, highlighting the importance of monitoring during treatment.
The FDA’s traditional approval of selpercatinib for RET fusion-positive thyroid cancer is a pivotal development, providing a new therapeutic option for patients with advanced or metastatic disease. The drug’s efficacy in both adult and pediatric populations, combined with its manageable safety profile, offers a promising treatment avenue for those who are refractory to existing therapies. As more data become available, selpercatinib’s role in the management of RET fusion-positive cancers will continue to evolve, potentially improving outcomes for many patients.
Resource: Food and Drug Administration, June 12, 2024
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