Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2026

Selpercatinib in pediatric and adolescent patients with RET-altered solid tumors: safety and efficacy results from the phase 1/2 LIBRETTO-121 study (145918)

Atsushi Manabe 1 , Theodore Laetsch 2 , Raquel Hladun Alvaro 3 , David Ziegler 4 , Hyoung Jin Kang 5 , Catherine Albert 6 , Tanya Watt 7 , Stephanie Fetzko 8 , Ayumu Arakawa 9 , Karsten Nysom 10 , Charlotte Rigaud 11 , Subha Suriyapperuma 12 , Nivedita Sharma 12 , Patrick Peterson 12 , Jennifer Wright 12 , Daniel Morgenstern 13 , Aarohan Pruthi 14
  1. Department of Pediatrics, Hokkaido University, Sapporo, Japan
  2. Children’s Hospital of Philadelphia and University of Pennsylvania, , Philadelphia, PA, USA
  3. Vall d'Hebron Institute of Research, Barcelona, Spain
  4. Kids Cancer Centre, Sydney Children’s Hospital, Randwick, NSW, Australia
  5. Department of Pediatrics, Seoul National University Children's Hospital, Seoul National University Cancer Research Institute, Seoul, Korea
  6. Seattle Children's Hospital, Seattle, WA, USA
  7. The University of Texas Southwestern Medical Center, Dallas, TX, USA
  8. Texas Children's Hospital, Baylor College of Medicine , Houston, TX, USA
  9. National Cancer Center Hospital, Tokyo, Japan
  10. Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark
  11. Gustave Roussy Cancer Campus, Paris-Saclay University, Villejuif , France
  12. Eli Lilly and Company, Indianapolis, IN, USA
  13. Hospital for Sick Children and University of Toronto, Toronto, ON, Canada
  14. Eli Lilly, Sydney, NSW, Australia

Aims

Selpercatinib is a highly selective oral RET inhibitor approved for treatment of RET-altered tumors in patients (pts) aged 12 years and older in Japan. We present final results from the LIBRETTO-121 study.

 

Methods

LIBRETTO-121 (NCT03899792) was a phase 1/2 trial in pts 0.5-21 yrs of age with advanced RET-altered solid tumors. Dosing started at 92 mg/m2 BID with no further escalation. Primary objectives were to evaluate safety and ORR (RECIST 1.1) by independent review committee (IRC).

Results

As of November 8, 2024, 36 pts aged 2-20 yrs were treated with selpercatinib, including 10 (27.8%) Asian pts. Tumor types were RET-mutant medullary thyroid cancer (n=15), RET fusion-positive papillary thyroid cancer (n=15), and other (n=6). Pts (n=36) treated with selpercatinib 92 mg/m2 (up to 160 mg BID) had a similar exposure as adults (n=667) treated with 160 mg BID at steady state on cycle 1 day 8. Time on selpercatinib was 0.4-62.4 mo; 25 pts remain on treatment. There were no DLTs or treatment discontinuations due to TEAEs. TEAEs of G3 or above included weight gain (11%), elevated ALT (8%), vomiting (8%), and anemia, constipation, hypertension, hypokalemia, and reduced neutrophil count (6% each). ORR (IRC) was 52.8% (19/36); 19.4% (7/36) had stable disease (CBR: 77.8% [28/36]). At 24 mo, the DOR was 100% (95% CI: 100, 100), and PFS rate was 86% (95% CI: 69%, 94%; mPFS: not reached; median follow-up: 30 mo).

Conclusions

Selpercatinib continues to show durable efficacy in pediatric and adolescent pts with RET-altered thyroid cancer and is tolerated with manageable toxicities.