The primary objective of Phase 1 is to determine the recommended Phase 2 dose (RP2D) of RXDX-105. The primary objective of Phase 1b is to further assess the safety profile and tolerability of RXDX-105 at the RP2D The secondary objective is to evaluate the antitumor activity of RXDX-105 at the RP2D, as assessed by objective response rate (ORR) (complete response [CR] or partial response [PR]) using Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) in patients with advanced solid tumors with RET or BRAF mutations or rearrangements.