First Experience Of Loxo-292 In The Management Of Pediatric Patients With Ret-Altered Cancers

10045 Background: Genomic alterations of RET kinase, including chromosomal fusions and activating point mutations, have been identified as oncogenic drivers in pediatric and adult cancers. Multikinase inhibitors have modest activity against RET-altered cancers and are associated with significant toxicity. LOXO-292 is a potent, ATP-competitive, small molecule RET inhibitor with high selectivity for RET, preclinical activity in the brain and excellent pharmacokinetic properties. In an ongoing phase 1/2 study of adult and adolescent patients with advanced RET-altered cancers, LOXO-292 demonstrated marked antitumor activity and was well tolerated. Methods: Pediatric patients with RET-altered cancers who were unable to access LOXO-292 through a phase 1/2 clinical trial were enrolled using FDA-allowed, IRB-approved single patient protocols . Patients received LOXO-292 (capsule/liquid formulation) orally, continuously, at a starting dose of 90 mg/m2 BID. Response was assessed locally by investigators. Results: As of January 31, 2019, 4 female patients aged 13 months–8 years were enrolled from the Republic of Korea (papillary thyroid cancer, n = 1) and the USA (infantile myofibroma/hemangiopericytoma, n = 1; congenital mesoblastic nephroma/infantile fibrosarcoma, n = 1; lipofibromatosis, n = 1). All tumors harbored RET gene fusions (5′ partners: CCDC6, MYH10, SPECC1L, and NCOA4, respectively), detected by next-generation sequencing. Previous therapies included surgery/iodine 131 (n = 1); vandetanib (n = 1); surgery/chemotherapy (n = 1); 1 patient was treatment-naïve. Duration of treatment ranged from 3–120 days and all patients remain on treatment. There were no dose modifications or discontinuations due to adverse events. There were no treatment-related adverse events ≥ grade 3. Two patients who were evaluable for response had partial responses (both ongoing, 1 confirmed, 1 pending confirmation). Conclusions: These preliminary data from a real-world setting suggest that LOXO-292 is effective and safe in pediatric patients whose tumors harbor RET gene fusions.