SUMMARY: The American Cancer Society estimates that for 2026, about 229,410 new cases of lung cancer will be diagnosed and 124,990 patients will die of the disease. Lung cancer is the leading cause of cancer-related mortality in the United States. Non-Small Cell Lung Cancer (NSCLC) accounts for approximately 85% of all lung cancers and adenocarcinoma is now the most frequent histologic subtype of lung cancer. The evolution of precision oncology in NSCLC continues to move beyond the metastatic setting, with targeted therapies increasingly demonstrating meaningful benefits in earlier stages of disease.
The Rationale for Targeting RET in Early Disease
RET kinase is a transmembrane Receptor Tyrosine Kinase and plays an important role during the development and maintenance of a variety of tissues, including neural and genitourinary tissues. RET signaling activates downstream pathways such as JAK/STAT3 and RAS/RAF/MEK/ERK and leads to cellular proliferation, survival, invasion, and metastasis. Oncogenic alterations to the RET proto-oncogene result in uncontrolled cell growth and enhanced tumor invasiveness. RET alterations include RET rearrangements, leading to RET fusions, and activating point mutations occurring across multiple tumor types. RET fusions have been identified in approximately 2% of NSCLCs, 10-20% of non-medullary thyroid cancers. Activating RET point mutations account for approximately 60% of sporadic Medullary Thyroid Cancers (MTC) and more than 90% of inherited MTCs. Other cancers with documented RET alterations include colorectal, pancreas, breast, and several hematologic malignancies.
Selpercatinib (RETEVMO®) is a highly selective and potent, CNS–penetrant RET inhibitor, designed to inhibit native RET signaling, as well as anticipated acquired resistance mechanisms. Selpercatinib selectively targets wild-type RET as well as various RET mutants and RET-containing fusion products. Additionally, Selpercatinib inhibits Vascular Endothelial Growth Factor Receptor 1 (VEGFR1), VEGFR3, Fibroblast Growth Factor Receptor 1 (FGFR1), FGFR2, and FGFR3. This results in inhibition of cell growth of tumors that exhibit increased RET activity. This agent has already demonstrated substantial clinical benefit in advanced and metastatic RET fusion–positive NSCLC, leading to its adoption as a standard targeted treatment in that setting.
While targeted therapies directed against EGFR mutations and ALK rearrangements have transformed postoperative management of early-stage NSCLC, patients with RET fusion–positive diseases have not previously had a comparable adjuvant treatment option. Consequently, recurrence following definitive therapy has remained a major concern.
LIBRETTO-432 was designed to determine whether earlier intervention with RET-directed therapy could alter the natural history of the disease and improve long-term outcomes.
Trial Design and Patient Population
LIBRETTO-432 was a global, randomized, double-blind, placebo-controlled Phase 3 study that enrolled 151 patients across 22 countries with Stage IB–IIIA RET fusion–positive NSCLC who had completed definitive locoregional treatment. Participants were randomized in a 1:1 ratio to receive either Sselpercatinib 160 mg twice daily (N=75) or Placebo (N=76) for up to three years. Importantly, the study allowed crossover from placebo to Selpercatinib in the event of disease recurrence, providing patients access to targeted therapy while also enabling assessment of adjuvant treatment benefit. Baseline characteristics were well balanced between treatment arms, ensuring robust comparisons between groups. The Primary endpoint was investigator-assessed Event Free Survival (EFS) in patients with Stage II–IIIA disease. Secondary endpoints included EFS in the overall study population, Blinded Independent Central Review (BICR)-assessed EFS, Overall Survival, and Safety. Median follow-up was 24 months for Selpercatinib and 27 months for Placebo.
Striking Reduction in Recurrence Risk
At the prespecified efficacy analysis, Selpercatinib demonstrated a profound and statistically significant improvement in EFS among patients with Stage II–IIIA disease. The risk of recurrence, progression, or death was reduced by approximately 83% compared with placebo, with a Hazard Ratio of 0.172 (P=0.0003). Median EFS was not reached in the Selpercatinib arm, whereas patients receiving placebo experienced a median EFS of 31.8 months. Only four EFS events occurred among patients receiving Selpercatinib compared with 19 events in the placebo group, underscoring the magnitude of benefit observed.
The separation of the survival curves was reflected in the 24-month EFS rates, which reached 91.5% with Selpercatinib compared with 61.1% with placebo. Independent Central Review confirmed these findings, demonstrating a consistent treatment effect and strengthening confidence in the robustness of the results.
Benefit Extends Across the Overall Study Population
The efficacy advantage observed in the primary analysis population was mirrored in the broader cohort of patients with Stage IB–IIIA disease. In the overall study population, Selpercatinib reduced the risk of an EFS event by approximately 84%, yielding a hazard ratio of 0.165 (P=0.0002). At two years, EFS rates were 93.8% in the Selpercatinib arm compared with 69.6% in the placebo group. The consistency of benefit across both primary and secondary analyses highlights the potential of RET inhibition to become an integral component of postoperative management for RET fusion–positive NSCLC.
Early Survival Signals and Crossover Experience
Although Overall Survival data remain immature, early observations are encouraging.
After a median follow-up of approximately 25 months in the Selpercatinib group, no deaths had been reported. In contrast, three deaths occurred in the placebo arm, all attributed to disease progression.
The crossover design provided valuable insight into treatment sequencing. Sixteen patients initially assigned to placebo crossed over to Selpercatinib after recurrence, with the majority remaining on treatment at the time of analysis. While crossover may ultimately dilute differences in Overall Survival between treatment groups, the substantial EFS benefit observed emphasizes the value of introducing targeted therapy before recurrence occurs.
Manageable Safety Profile Consistent With Prior Experience
The safety findings from LIBRETTO-432 were generally consistent with the established profile of Selpercatinib in advanced RET fusion–positive NSCLC. The most commonly reported grade 3 or higher toxicities included elevations in liver enzymes, specifically ALT and AST, as well as hypertension. Most events were manageable through dose modifications and routine clinical monitoring. Treatment discontinuation due to adverse events occurred in 17.3% of patients receiving Selpercatinib, compared with 1.3% of those receiving placebo. Importantly, no deaths occurred during assigned study treatment, and all reported deaths were confined to the placebo arm as a consequence of disease progression.
These findings suggest that while long-term therapy requires careful toxicity management, the benefit-risk profile remains favorable in light of the substantial reduction in recurrence risk.
Reinforcing the Importance of Comprehensive Biomarker Testing
One of the most important implications of LIBRETTO-432 extends beyond the efficacy of Selpercatinib itself. The study reinforces the necessity of comprehensive genomic profiling at the time of NSCLC diagnosis, regardless of disease stage.
Historically, molecular testing has often been prioritized in advanced disease where treatment decisions depend heavily on biomarker status. However, the emergence of effective adjuvant targeted therapies across multiple genomic subsets, including EGFR, ALK, and now potentially RET, demonstrates that molecular characterization has become equally critical in early-stage disease. Failure to identify actionable alterations at diagnosis may result in missed opportunities to offer therapies capable of substantially reducing recurrence risk and improving long-term outcomes.
Looking Ahead
The success of LIBRETTO-432 reflects a broader transformation in thoracic oncology. Increasingly, therapies initially developed for metastatic disease are being evaluated in earlier-stage settings where the potential impact on cure is greatest. LIBRETTO-432 is the first randomized Phase 3 study to evaluate a RET inhibitor in the adjuvant setting for early-stage RET fusion–positive NSCLC, and its results represent a major advance for this patient population.
With an approximately 83% reduction in the risk of recurrence, progression, or death, Selpercatinib delivered a clinically meaningful and statistically significant improvement in Event-Free Survival while maintaining a manageable safety profile. These findings position adjuvant Selpercatinib as a potential new standard of care for patients with resected RET fusion–positive NSCLC.
Event-free survival with adjuvant selpercatinib in stage IB-IIIA RET fusion-positive NSCLC: Primary results of the phase 3 LIBRETTO-432 trial. Goldman JW, Yang X, Hochmair M, et al. J Clin Oncol 44, 2026 (suppl 17; abstr LBA3)
