Lifirafenib is an investigational, reversible inhibitor of B-RAF, wild-type A-RAF, B-RAF, C-RAF, and EGFR. This first-in-human, phase I, dose-escalation/dose-expansion study evaluated the safety, tolerability, and efficacy of lifirafenib in patients with – or -mutated solid tumors.
During dose escalation, adult patients with histologically/cytologically confirmed advanced solid tumors received escalating doses of lifirafenib. Primary end points were safety/tolerability during dose escalation and objective response rate in preselected patients with and mutations during dose expansion.
The maximum tolerated dose was established as 40 mg/d; dose-limiting toxicities included reversible thrombocytopenia and nonhematologic toxicity. Across the entire study, the most common grade ≥ 3 treatment-emergent adverse events were hypertension (n = 23; 17.6%) and fatigue (n = 13; 9.9%). One patient with -mutated melanoma achieved complete response, and 8 patients with mutations had confirmed objective responses: melanoma (n = 5, including 1 patient treated with prior B-RAF/MEK inhibitor therapy), thyroid cancer/papillary thyroid cancer (PTC; n = 2), and low-grade serous ovarian cancer (LGSOC; n = 1). One patient with -mutated non-small-cell lung cancer (NSCLC) had unconfirmed partial response (PR). Patients with -mutated endometrial cancer and codon 12-mutated NSCLC had confirmed PR (n = 1 each). No responses were seen in patients with -mutated colorectal cancer (n = 20).
Lifirafenib is a novel inhibitor of key RAF family kinases and EGFR, with an acceptable risk-benefit profile and antitumor activity in patients with -mutated solid tumors, including melanoma, PTC, and LGSOC, as well as -mutated NSCLC and endometrial carcinoma. Future comparisons with first-generation B-RAF inhibitors and exploration of lifirafenib alone or as combination therapy in patients with selected mutations who are resistant/refractory to first-generation B-RAF inhibitors are warranted.