Impact of trough concentrations of regorafenib and its major metabolites M-2 and M-5 on overall survival of chemorefractory metastatic colorectal cancer patients: Results from a multicentre GERCOR TEXCAN phase II study

This prospective pharmacokinetic (PK) ancillary study of the TEXCAN phase II GERCOR trial of patients with chemorefractory metastatic colorectal cancer and treated with regorafenib (REGO) investigated correlations between overall survival (OS) and concentrations (C) of REGO and its active metabolites, M-2 and M-5.55 patients received REGO 160 mg/day for 21 days of a 28-day cycle (NCT02699073). REGO, M-2, M-5 were measured by liquid chromatography-mass spectrometry assay on day 15 of cycle 1 (C1) and 2 (C2). We studied the association between OS and Cmin of REGO, M-2 and M-5 at C1 and their accumulations between C1 and C2.Medians of C2/C1 M-2 and M-5 ratios were 0.82 (interquartile range 0.50-1.78) and 0.75 (interquartile range 0.41-1.93), respectively. Patients with C2/C1 M-2 ratio ≥ median had improved survival compared to those < median (12.6 versus 4.0 months, P = 0.023), corresponding to a 66% mortality risk reduction in multivariate analysis. The C2/C1 M-2 ratio correlated with C1 REGO+M-2+M-5 (Csum; P = 0.006). Restricted cubic spline analysis showed an increased OS benefit as the C2/C1 M-2 ratio raises and when C1 Csum ranged between 2.5 and 5.5 mg/L. Patients within the Csum range had a reduced incidence of serious adverse events and improved OS.We identified PK parameters associated with a survival benefit in patients with metastatic colorectal cancer treated by REGO. OS and safety were favourable when C1 REGO+M-2+M-5 Csum ranged between 2.5 and 5.5 mg/L. These results pave the way for individual REGO dose modification strategies based on PK monitoring.NCT02699073.