The aim of this study is to investigate: bortezomib PK after single and multiple dose treatment; the mechanisms behind the observed changes in the PK parameters after repeated dosing; any clinically plausible intrinsic factors that may explain and reduce variability; the relationship between body weight/ body surface area/ lean body weight) and PK parameters since dosing regimen is based on BSA; the concentration-proteasome inhibition relationship using PK/ PD-modelling;