Lilly’s Retevmo Shows Superior Survival in Phase III Thyroid Cancer Trial

Pictured: Eli Lilly sign on building/iStock, jetcityimage

Pictured: Eli Lilly sign on building/iStock, jetcityimage

Eli Lilly has scored a win against its competitors in the narrow but focused space of rearranged during transfection (RET)-mutant medullary thyroid cancer. The drugmaker announced topline results Tuesday showing that Retevmo (selpercatinib), its FDA-approved RET kinase inhibitor, beat out Exelixis’ Cabometyx (cabozantinib) and Sanofi’s Caprelsa (vandetanib) in progression-free survival based on late-stage clinical trial results.

Lilly’s Phase III LIBRETTO-531 trial tested its RET kinase inhibitor against the first-line multikinase inhibitor treatments, evaluating the relative efficacy and safety of the drugs. The drugmaker said Retevmo beat out the other two treatments in progression-free survival—the primary endpoint of the study—based on a pre-specified interim efficacy analysis conducted by an independent data monitoring committee.

The trial also had secondary endpoints of treatment failure-free survival, overall response rate, duration of response, and overall survival. Lilly’s press release did not mention whether any of these endpoints were met in the study.

Lilly did note in the announcement that adverse events observed in LIBRETTO-531 “were generally consistent with those identified across the previously reported Retevmo development program.” Retevmo’s labeling contains warnings and precautions for hepatotoxicity, interstitial lung disease/pneumonitis, hypertension, QT interval prolongation, hemorrhagic events, hypersensitivity, tumor lysis syndrome, risk of impaired wound healing, hypothyroidism and embryo-fetal toxicity.

David Hyman, chief medical officer of Loxo Oncology, a wholly-owned subsidiary of Lilly, said in a statement that the “data from the LIBRETTO-531 trial confirm the importance of selectivity in targeting RET-driven cancers and suggest Retevmo should be considered the preferred first-line treatment for people with advanced RET-mutant medullary thyroid cancer.”

According to Lilly, medullary thyroid cancer (MTC) accounts for just 1% to 2% of thyroid cancers in the U.S., while RET mutations are found in approximately 60% of sporadic MTC and over 90% of hereditary MTC.

The win comes on the heels of other good news for Retevmo, which recently demonstrated in the LIBRETTO-431 trial superior progression-free survival for patients with RET fusion-positive advanced or metastatic non-small cell lung cancer (NSCLC) compared to platinum-based chemotherapy combined with pemetrexed and/or pembrolizumab.

Tuesday’s topline results from the LIBRETTO-531 trial also marks something of a coup for Lilly against Roche, which recently withdrew its own RET-mutant medication Gavreto, co-developed with Blueprint Medicines. In a June 30 SEC filing, Blueprint said a planned Phase III trial would “no longer be pursued due to feasibility.” This decision came not long after Roche decided to end its partnership with Blueprint in February this year, which takes effect in February 2024, and will hand Gavreto back.

Both results build on Lilly’s LIBRETTO-001 trial, which is treating RET-driven cancers with Retevmo, with the company saying in a September 2022 release that the drug “demonstrated clinically meaningful and durable responses across a variety of tumor types” including pancreatic, colon and other cancers.

Connor Lynch is a freelance writer based in Ottawa, Canada. Reach him at

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