A phase I/IB trial of the vegfr-sparing multikinase ret inhibitor RXDX-105

Alexander Drilon, Siqing Fu, Manish R. Patel, Marwan Fakih, Ding Wang, Anthony J. Olszanski, Daniel Morgensztern, Stephen V. Liu, Byoung Chul Cho, Lyudmila Bazhenova, Cristina P. Rodriguez, Robert C. Doebele, Antoinette Wozniak, Karen L. Reckamp, Tara Seery, Petros Nikolinakos, Zheyi Hu, Jennifer W. Oliver, Denise Trone, Katherine McArthurRupal Patel, Pratik S. Multani, Myung Ju Ahn

Research output: Contribution to journalArticlepeer-review

91 Scopus citations


RET fusions are oncogenic drivers of various tumors, including non–small cell lung cancers (NSCLC). The safety and antitumor activity of the multikinase RET inhibitor RXDX-105 were explored in a phase I/Ib trial. A recommended phase II dose of 275 mg fed daily was identified. The most common treatment-related adverse events were fatigue (25%), diarrhea (24%), hypophosphatemia (18%), maculopapular rash (18%), and nonmaculopapular rash (17%). In the phase Ib cohort of RET inhibitor–naïve patients with RET fusion–positive NSCLCs, the objective response rate (ORR) was 19% (95% CI, 8%–38%, n = 6/31). Interestingly, the ORR varied significantly by the gene fusion partner (P < 0.001, Fisher exact test): 0% (95% CI, 0%–17%, n = 0/20) with KIF5B (the most common upstream partner for RET fusion–positive NSCLC), and 67% (95% CI, 30%–93%, n = 6/9) with non-KIF5B partners. The median duration of response in all RET fusion–positive NSCLCs was not reached (range, 5 to 18+ months). SIGNIFICANCE: Although KIF5B-RET is the most common RET fusion in NSCLCs, RET inhibition with RXDX-105 resulted in responses only in non– KIF5B–RET- containing cancers. Novel approaches to targeting KIF5B-RET- containing tumors are needed, along with a deeper understanding of the biology that underlies the differential responses observed.

Original languageEnglish
Pages (from-to)384-395
Number of pages12
JournalCancer discovery
Issue number3
StatePublished - Mar 1 2019


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