Towards new methods for the determination of dose limiting toxicities and the assessment of the recommended dose for further studies of molecularly targeted agents – Dose-Limiting Toxicity and Toxicity Assessment Recommendation Group for Early Trials of Targeted therapies, an European Organisation for Research and Treatment of Cancer-led study

Introduction Traditional dose-limiting toxicity (DLT) definition, which uses grade (G) 3–4 toxicity data from cycle 1 (C1) only, may not be appropriate for molecularly targeted agents (MTAs) of prolonged administration, for which late or lower grade toxicities also deserve attention. Patients and methods In collaboration with pharmaceutical companies and academia, an European Organisation for Research and Treatment of Cancer (EORTC)-led initiative, Dose-Limiting Toxicity and Toxicity Assessment Recommendation Group for Early Trials of Targeted therapies (DLT-TARGETT), collected data from completed phase 1 trials evaluating MTAs as monotherapy. All toxicities at least possibly related to the study drugs that occurred during C1–6, their type, grade (CTCAEv3.0), and duration as well as patients' relative dose-intensity (RDI), were recorded. Results The 54 eligible trials enrolled 2084 evaluable adult patients with solid tumours between 1999 and 2013, and evaluated small molecules (40), antibodies (seven), recombinant peptides (five) and antisense oligodeoxynucleotides (two). A maximum tolerated dose was set in 43 trials. Fifteen percent of the patients received <75% of the intended RDI in C1, but only 9.1% of them presented protocol-defined DLTs. After C1, 16–19% of patients received <75% of the intended RDI. A similar proportion of G ⩾ 3 toxicities was recorded in C1 and after C1 (936 and 1087 toxicities, respectively), with the first G ⩾ 3 toxicity occurring after C1 in 18.6% of patients. Conclusion Although protocol-defined DLT period is traditionally limited to C1, almost 20% of patients present significant reductions in RDI at any time in phase 1 trials of MTAs. Recommended phase 2 dose assessment should incorporate all available information from any cycle (notably lower grade toxicities leading to such RDI decrease), and be based on achieving >75% RDI.