Lilly's Selpercatinib Meets Primary Endpoint in Adjuvant Lung Cancer Trial, a First for RET-Targeted Therapy
Eli Lilly announced positive topline results from the Phase III LIBRETTO-432 trial evaluating Retevmo (selpercatinib), a selective RET kinase inhibitor, as adjuvant therapy in patients with early-stage (stage II–IIIA) RET fusion-positive non-small cell lung cancer (NSCLC). The trial met its primary endpoint, demonstrating a statistically significant improvement in investigator-assessed event-free survival compared with placebo. The selpercatinib adjuvant lung cancer data mark the first time a selective RET inhibitor has shown efficacy in the post-surgical setting, extending the drug's clinical profile beyond the advanced disease context in which it was originally approved.
The result carries implications beyond the RET fusion-positive population itself. It reinforces a broader pattern in thoracic oncology: that targeted therapies validated in metastatic NSCLC can deliver measurable benefit when deployed earlier in the disease course, following the precedent set by EGFR- and ALK-directed agents. It also sharpens the case for routine genomic testing at diagnosis across all stages of lung cancer, a practice that remains inconsistent in clinical settings worldwide.
Trial Specifics: LIBRETTO-432 Trial Results and Selpercatinib Event-Free Survival
LIBRETTO-432 is a global, multicenter, randomized, double-blind, placebo-controlled Phase III study. It enrolled 151 patients with RET fusion-positive NSCLC who had completed definitive surgery or radiotherapy with curative intent, along with any other indicated adjuvant therapy. Patients were randomized 1:1 to receive either selpercatinib or placebo. Selpercatinib was dosed orally twice daily at 120 mg (for patients weighing less than 50 kg) or 160 mg (for those at or above 50 kg), consistent with the drug's approved dosing regimen in the advanced setting.
The primary endpoint was event-free survival as assessed by the investigator in the primary analysis population of stage II–IIIA patients. Lilly described the result as "highly statistically significant and clinically meaningful," indicating a reduction in the risk of disease recurrence or death. The company did not disclose the hazard ratio, confidence interval, or specific p-value in its topline announcement. Overall survival data trended in favor of selpercatinib but were immature at the time of analysis, with few events observed — an expected finding given the early-stage population and the typical timeline required for OS maturation.
Secondary endpoints included EFS by blinded independent central review, overall survival, time to distant CNS recurrence, progression-free survival on the next line of treatment, and the positive predictive value of RET testing methodologies. The safety profile was described as generally consistent with prior selpercatinib trials, including the registrational LIBRETTO-001 and LIBRETTO-431 studies. Known risks associated with selpercatinib include hepatotoxicity, hypertension, QT prolongation, interstitial lung disease, and hemorrhagic events.
Lilly said it plans to present detailed results at an upcoming medical congress and submit the data to a peer-reviewed journal. The company also indicated it would discuss the findings with health authorities globally, signaling intent to pursue regulatory submissions for the adjuvant indication. Jacob Van Naarden, executive vice president and president of Lilly Oncology, stated: "The LIBRETTO-432 results support this observation, demonstrating an effect size in line with the most striking data for targeted adjuvant therapy in lung cancer." He added that the company hopes the results "further accelerate the use of genomic testing for all people diagnosed with early-stage disease."
Research Context: Selpercatinib Adjuvant Lung Cancer and the RET Fusion Landscape
Selpercatinib is a selective, oral inhibitor of the RET (rearranged during transfection) kinase, designed to block the oncogenic signaling driven by RET gene fusions and activating mutations. RET fusions occur in approximately 1% to 2% of all NSCLC cases and are predominantly mutually exclusive from other oncogenic drivers such as EGFR mutations or ALK rearrangements. When a RET fusion is present, the resulting chimeric protein drives constitutive kinase activity, promoting tumor cell proliferation and survival. By selectively inhibiting RET, selpercatinib disrupts this signaling axis. The drug also has documented central nervous system activity, a relevant property given the propensity of NSCLC to metastasize to the brain.
Retevmo received its initial US FDA approval in 2020 under accelerated approval for adult patients with metastatic RET fusion-positive NSCLC, based on data from the LIBRETTO-001 basket trial. It subsequently gained regular approval following the LIBRETTO-431 Phase III trial, which demonstrated superiority over chemotherapy with or without pembrolizumab as first-line treatment in advanced RET fusion-positive NSCLC. The drug is also approved for RET-mutant medullary thyroid cancer and RET fusion-positive thyroid cancer.
The adjuvant early-stage NSCLC treatment setting explored in LIBRETTO-432 is distinct from these prior indications. NSCLC accounts for roughly 85% of all lung cancer diagnoses in the United States, and approximately 30% of patients present with stage IB–IIIA disease, where surgery with curative intent is the standard approach. Despite resection, recurrence rates remain substantial, creating a rationale for adjuvant systemic therapy. The success of osimertinib (AstraZeneca's EGFR inhibitor) in the ADAURA trial for EGFR-mutant early-stage NSCLC, and of alectinib (Roche) in the ALINA trial for ALK-positive early-stage NSCLC, established the paradigm that targeted adjuvant therapy can delay or prevent recurrence in biomarker-defined lung cancer populations. LIBRETTO-432 now extends this paradigm to RET fusion-positive lung cancer.