BT062 is an immunoconjugate consisting of anti CD138 antibody and cytotoxic agent maytansinoid DM4. CD138 is over-expressed on multiple myeloma cells compared to normal plasma cells. BT062 will be administered on days 1, 8 and 15 with Lenalidomide once daily on days 1-21 in patients with relapsed or refractory multiple myeloma.