ABCB1 and Miyoshi myopathy: This theory is consistent with the observation that the MTD of nelfinavir in combination with bortezomib (a poor MDR-1 substrate) and dexamethasone was 2 × 2500 mg/day (ref. 8), while in our present study the MTD was only 2 × 1250 mg in combination with lenalidomide–dexamethasone in a comparable population of MM patients.