Phase 3 LIBRETTO-531 trial : Lilly’s Retevmo meets primary endpoint of PFS

Eli Lilly and Company (NYSE: LLY) unveiled exceptional results from their LIBRETTO-531 study of Retevmo (selpercatinib), setting a new standard in the treatment of advanced RET-mutant medullary thyroid cancer (MTC). The Phase 3 clinical trial distinctly highlights Retevmo’s superiority over existing first-line treatments, namely multikinase inhibitors cabozantinib and vandetanib. Retevmo demonstrated a statistically significant and clinically meaningful improvement in progression-free survival (PFS), based on a pre-specified interim efficacy analysis.

Retevmo’s unprecedented results were further scrutinized and endorsed by an independent data monitoring committee (IDMC). This breakthrough development in medullary thyroid cancer treatment holds monumental implications, as adverse events from Retevmo aligned with those observed in prior Retevmo studies, namely LIBRETTO-001, LIBRETTO-121, and LIBRETTO-321.

The spotlight of this achievement goes beyond just medullary thyroid cancer. David Hyman, Chief Medical Officer at Loxo@Lilly, emphasized that these findings “confirm the importance of selectivity in targeting RET-driven cancers.” He further suggested that Retevmo should be the go-to first-line treatment for patients with advanced RET-mutant MTC. This remarkable efficacy also complements the recent positive outcomes from Retevmo Phase 3 LIBRETTO-431 studies in lung cancer.

LIBRETTO-531 is the first-of-its-kind randomized, open-label clinical trial directly comparing the safety and effectiveness of a highly selective RET-kinase inhibitor like Retevmo against multikinase inhibitors. With 291 patients enrolled, participants were given either Retevmo or a physician’s choice of cabozantinib or vandetanib. Secondary endpoints included treatment failure-free survival (TFFS), overall response rate (ORR), duration of response (DoR), and overall survival (OS).

Retevmo’s clinical prowess is not a standalone event; it builds upon the extensive data garnered from LIBRETTO-001, the largest clinical trial involving RET-driven cancers treated with a RET inhibitor. Spanning 16 countries and 85 sites, this study included more than 800 patients and showed Retevmo’s profound and durable responses across diverse tumor types.

Medullary thyroid cancer accounts for 1-2% of all thyroid cancers in the United States, with RET mutations detected in around 60% of sporadic MTC cases and over 90% in hereditary MTC. The LIBRETTO-531 study, therefore, holds vital importance for a subset of the population vulnerable to this cancer type. Full results will be presented at an upcoming medical meeting, submitted to peer-reviewed journals, and discussed with healthcare authorities.

Finally, it’s worth noting that Retevmo is already a US FDA-approved oral prescription medicine, taken twice daily until disease progression or unacceptable toxicity occurs. With dosages varying based on patient weight, Retevmo stands as a potent and highly selective RET kinase inhibitor with CNS activity. Given its exceptional efficacy in enhancing progression-free survival in RET-mutant medullary thyroid cancer, Retevmo is poised to become the new standard of care in this domain.