The present invention providesmelflufen (melphalan flufenamide； L-Melphalanyl-4-fluoro-L-phenylalanine ethyl ester), or a salt thereof, for use in the treatment or prophylaxis of multiple myeloma, wherein a dosage of melflufen (excluding the mass of any salt) is administered as a parenteral dosage at an infusion rate of 1.0 to 1.8 mg/min. Also provided is melflufen, or a salt thereof, for use in the treatment or prophylaxis of a cancer, for example a solid cancer, wherein a dosage of melflufen is administered as a parenteral dosage at an infusion rate less than 0.8 mg/min (for example 0.3 to 1.0 mg/minor for example 0.3 to 0.8 mg/min).
