A Study of Oral LOXO-292 (Selpercatinib) in Pediatric Participants With Advanced Solid or Primary Central Nervous System (CNS) Tumors

This is an open-label, multi-center Phase 1/2 study of oral LOXO-292 in pediatric participants with an activating rearranged during transfection (RET) alteration and an advanced solid or primary CNS tumor.

This study includes 2 parts: phase 1 (dose escalation) and phase 2 (dose expansion). In phase 1, participants will be enrolled using a rolling 6 dose escalation scheme. The starting dose of LOXO-292 is equivalent to the adult recommended phase 2 dose of 160 milligrams (mg) twice a day (BID). Once the maximum tolerated dose (MTD) and/or recommended phase 2 dose (RP2D) is identified, participants will be enrolled to one of four phase 2 dose expansion cohorts depending on tumor histology and tumor genotype. Cycle length will be 28 days.

Inclusion Criteria: * Advanced or metastatic solid or primary CNS tumor which has failed standard of care therapies * Evidence of an activating RET gene alteration in the tumor and/or blood * Measurable or non-measurable disease * Karnofsky (participants 16 years and older) or Lansky (participants younger than 16) performance score of at least 50 * Participant with primary CNS tumors or cerebral metastases must be neurologically stable for 7 days prior and must not have required increasing doses of steroids within the last 7 days * Adequate hematologic, hepatic and renal function. * Ability to receive study drug therapy orally or via gastric access * Willingness of men and women of reproductive potential to observe conventional and effective birth control Exclusion Criteria: * Major surgery within two weeks prior to planned start of LOXO-292 * Clinically significant, uncontrolled cardiac, cardiovascular disease or history of myocardial infarction within 6 months prior to planned start of LOXO-292 * Active uncontrolled systemic bacterial, viral, fungal or parasitic infection * Clinically significant active malabsorption syndrome * Pregnancy or lactation * Uncontrolled symptomatic hyperthyroidism or hypothyroidism (i.e. the participant required a modification to current thyroid medication in the 7 days before start of LOXO-292) * Uncontrolled symptomatic hypercalcemia or hypocalcemia * Known hypersensitivity to any of the components of the investigational agent, LOXO-292 or Ora-Sweet® SF and OraPlus®, for participants who will receive LOXO-292 suspension * Prior treatment with a selective RET inhibitor(s) (including investigational selective RET inhibitor\[s\])