A dose-escalating phase I of imatinib mesylate with fixed dose of metronomic cyclophosphamide in targeted solid tumours
Preclinical findings suggest that imatinib mesylate (IM) and metronomic cyclophosphamide (MC) combination provides synergistic antiangiogenic activity on both pericytes and endothelial cells. We have designed a 3+3 dose-escalating phase I trial with a fixed dose of MC (50 mg two times daily) plus IM (400 mg per day; 300 and 400 mg two times daily). Enrolled patients had IM- and sutininib-refractory advanced gastrointestinal stromal tumours (GIST) (n=17), chordoma (n=7) and mucosal melanoma (n=2). Dose-limiting toxicities were monitored for the first 6 weeks. Progression-free survival (PFS) and response assessment are based on RECIST 1.0 guidelines. Pharmacokinetics of IM were measured before and after exposure to MC. No dose-limiting toxicity was observed. Fourteen patients of the expanded cohort received 400 mg two times daily of IM with MC. Apart from a case of possibly related acute leukaemia occurring after 4 years of treatment, we did not see unexpected toxicity. No drug-drug pharmacokinetic interaction was observed. There was no objective response. We have observed long-lasting stable disease in chordoma patients (median PFS=10.2 months; range, 4.2-18+) and short-term stable disease in heavily GIST pretreated patients (median PFS=2.3 months; range, 2.1-6.6). This combination is feasible and may warrant further exploration in refractory GIST or chordoma patients.