Of the 13 286 autologous haematopoietic cell transplant procedures reported in the US in 2010-2012 for plasma cell disorders, 10 557 used single agent, high-dose melphalan. Despite 30 years of clinical and pharmacokinetic (PK) experience with high-dose melphalan, and its continuing central role as cytoreductive therapy for large numbers of patients with myeloma, the pharmacodynamics and pharmacogenomics of melphalan are still in their infancy. The addition of protectant agents such as amifostine and palifermin allows dose escalation to 280 mg/m 2 , but at these doses it is cardiac, rather than gut, toxicity that is doselimiting. Although combination with additional alkylating agents is feasible, the additional TRM may not be justified when so many post-consolidation therapies are available for myeloma patients. Current research should optimise the delivery of this single-agent chemotherapy. This includes the use of newer formulations and real-time PKs. These strategies may allow a safe and effective platform for adding synergistic novel therapies and provide a window of lymphodepletion for the addition of immunotherapies. To best assess the contribution that the dose of drug makes to clinically meaningful endpoints in haematopoietic cell transplantation (HCT), one would choose one drug, ideally used as monotherapy, for one disease and with one source of haematopoietic progenitor cells (HPC). Although this approach may appear quite restrictive, these criteria are fulfilled when high-dose melphalan is used in the context of autologous HCT for plasma cell myeloma. Indeed, melphalan, which has been in use for 60 years, has been used in this way for 30 years. One might think we would know all there is to know about the use of this agent for this indication. However, in fact, we know very little. Several years ago, we briefly reviewed this subject, but the focus was on the various settings in which high-dose melphalan and autologous HCT were used. 1 In this present review, we will not discuss the role of high-dose melphalan in HCT but would direct readers to an excellent recent review on this topic. 2 Instead, we will use that review as our starting point for what we know about the pharmacokinetics (PK) of melphalan for high-dose therapy, in particular for myeloma, and how we may move forward.
EARLY WORKHigh-dose melphalan has been in use for decades. The relatively few and reversible non-hematologic toxic effects make it suitable for high-dose therapy, whereas its profound marrow toxicity makes it unsuitable for repeated low-dose exposures. Today, most patients are naïve to melphalan exposure as it is only infrequently used as initial cancer therapy. The toxicity profile means that infusion of HPC can rescue or protect against most of the toxicity of the drug-hence, melphalan is the ideal agent for high-dose therapy with rescue by autologous HCT.Amongst the variety of solid tumours for which subjects first underwent HCT using melphalan were paediatric patients with neuroblastoma; these early reports garnered the inte...