CD38 and Miyoshi myopathy: It has been previously shown that PC loose P-gp function when they home to the bone marrow and re-activate it again while leaving the marrow.23 Further, it has been shown that malignant MM cell population of patients relapsing under PI treatment consist of multiple subclones with different maturation stages within each subclone, from CD138+,CD38+ to CD138−,CD38−,CD20+ MM cells;15 therefore, gene expression profiling analysis of CD138+ cells is likely not representative of the whole PI-resistant population.