Multicenter, single-arm, phase II study of the continuous use of panitumumab in combination with FOLFIRI after FOLFOX for RAS wild-type metastatic colorectal cancer: Exploratory sequential examination of acquired mutations in circulating cell-free DNA

This multicenter single-arm, phase II study evaluated the efficacy and safety of uninterrupted panitumumab usage combined with cytotoxic doublets for unresectable/metastatic colorectal cancer (mCRC). Additionally, clinical value of the RAS/BRAF mutation status in circulating cell-free DNA (ccfDNA) was evaluated; this evaluation was measured independently of the protocol treatment. Eligible patients with RAS wild-type mCRC who had received the first-line panitumumab plus FOLFOX treatment were recruited and administered continuous panitumumab combined with FOLFIRI. Progression-free survival (PFS) at 6 months was the primary endpoint, with threshold and expected values of 35% and 50%, respectively. In total, 54 patients were enrolled between October 2017 and October 2019. The crude 6-month PFS rate was 37.0%, with a 4.8-month median PFS. The response rate and disease control rate were 16.7% and 50.0%, respectively. Notably, of the 54 participants, 17 showed RAS/BRAF mutations until the end of the protocol treatment and of the 22 patients with progressive disease as their best response, 10 possessed RAS/BRAF mutations in their plasma ccfDNA at baseline. The median PFS significantly differed among patients harboring tumors with BRAF and RAS mutations and those with wild-type tumors. In conclusion, our study failed to show the expected efficacy of the continuous panitumumab use in the second-line treatment. Liquid biopsy discriminated the duration of PFS according to the mutation status. The effectiveness of continuous treatment with panitumumab should be evaluated in patients with RAS/BRAF wild-type mCRC determined by liquid biopsy at the start of the second-line treatment.