A case report of a patient with end-stage relapsed/refractory MM showed that the addition of tadalafil to its treatment regimen (lenalidomide, clarithromycin, dexamethasone) reduced the MDSC suppressive activity, as illustrated by a reduction in IL4Rα+, iNOS, Arg-1 and ROS. The gene discussed is ARG1; the disease is Miyoshi myopathy.