Background: Entrectinib is a potent oral inhibitor of the tyrosine kinases TrkA, TrkB, TrkC (encoded by the genes NTRK1, NTRK2, NTRK3, respectively), ROS1, and ALK with IC50 < 2 nM (biochemical kinase assay). It has been evaluated in two Phase 1 studies (STARTRK-1 and ALKA-372-001) in patients with advanced or metastatic solid tumors harboring NTRK1/2/3, ROS1, or ALK molecular alterations, with or without asymptomatic or controlled CNS disease. Previously, we reported 600 mg daily as the Recommended Phase 2 Dose (RP2D) and an objective response rate of 72% in 18 tyrosine kinase inhibitor (TKI)-naïve patients with NTRK1/2/3 (4), ROS1 (8), or ALK (6) rearrangements treated at or above the RP2D (Siena et al, ESMO 2015).

Methods: A 3+3 dose escalation was used to assess safety, pharmacokinetics, and identify the RP2D of entrectinib. Here we provide an update on anti-tumor activity (RECIST v1.1) and safety with continued follow-up of the cohort of patients with gene rearrangements.

Results: At a median follow-up of 11 months, 11 of the 18 patients remain on study. Objective responses were observed in 3 of 4 (75%) NTRK1/2/3, 6 of 8 (75%; 1 complete response) ROS1 and 4 of 6 (67%) ALK patients, respectively. Responses were observed in NSCLC, colorectal cancer, mammary analog secretory carcinoma, and other solid tumors, as early as cycle 1 and lasting as long as > 2 years. Notably, a 46-year old male patient with SQSTM1-NTRK1-rearranged NSCLC previously treated with 4 lines of chemotherapy and immunotherapy achieved an overall partial response with a complete response in the brain. He remains on study in response at 10 months. The most common (>10%) treatment-related adverse events (AEs) at the RP2D were fatigue/asthenia (47%), dysgeusia (32%), constipation (26%), dizziness (21%), paresthesia (21%), diarrhea (16%), myalgia (16%), and weight gain (16%). Three treatment-related serious AEs were reported (2 occurred above the RP2D); all resolved with dose modifications.

Conclusions: Entrectinib continues to display promising anti-tumor activity in TKI-naive patients across different solid tumor types harboring an NTRK1/2/3, ROS1, or ALK gene rearrangement. Similar patients are now being enrolled in STARTRK-2, a global Phase 2 basket study of entrectinib.

Citation Format: Alexander Drilon, Filippo G. De Braud, Salvatore Siena, Sai-Hong I. Ou, Manish Patel, Myung-Ju Ahn, Jeeyun Lee, Todd M. Bauer, Anna F. Farago, Stephen V. Liu, Natasha Reddinger, Rupal Patel, David Luo, Edna Chow Maneval, Pratik S. Multani, Robert C. Doebele, Alice T. Shaw. Entrectinib, an oral pan-Trk, ROS1, and ALK inhibitor in TKI-naïve patients with advanced solid tumors harboring gene rearrangements: Updated phase I results. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT007.