Small bowel edema and lymphocytic duodenitis as severe reversible gastrointestinal toxicity of selpercatinib in RET fusion–positive non–small cell lung cancer: a case report

INTRODUCTION: Rearranged during transfection (RET) gene rearrangements occur in 1%–2% of non–small cell lung cancer (NSCLC). Because of the results of the study LIBRETTO-001, selpercatinib has been approved as the first-line treatment for patients with RET fusion–positive advanced NSCLC. Selpercatinib demonstrated to be well tolerated. Despite this, gastrointestinal adverse events (AEs) are frequently reported, and no clinical-radiological and endoscopic features and their impact in terms of treatment discontinuations, interruptions, and dose reductions have been described so far. CASE REPORT: A 37-year-old never-smoker woman was treated in our institution with selpercatinib for a RET fusion–positive NSCLC. After 9 months of treatment, the patient referred abdominal pain of grade (G) 2, associated with nausea of G2, bilious vomiting of G3, and weight loss of G1. At computed tomography scan, the presence of important bowel wall thickening, free ascitic fluid, mesenteric congestion, and stranding was detected. The patient underwent an anterograde enteroscopy extended to jejunum with detection of lymphocytic duodenitis with sub-mucosal edema. Selpercatinib treatment was temporary interrupted with complete resolution of the symptoms and then re-administered with dose reduction, without relapsed of the gastrointestinal toxicity after 120 days. CONCLUSION: To our knowledge, this is the first case report of a patient with NSCLC treated with selpercatinib outside a clinical study who developed severe gastrointestinal toxicity characterized by small bowel edema and lymphocytic duodenitis, leading to treatment interruption and dose reduction. The gastrointestinal AE has been described by a radiological, endoscopic, and histopathological point of view. Further investigations are needed to better identify pathological mechanisms of gastrointestinal toxicity for an appropriate AE management.