MS4A1 and non-Hodgkin lymphoma: Two anti-CD20 mAbs, ibritumomab tiuxetan radiolabeled with yttrium-90 (Zevalin®, Spectrum Pharmaceuticals, USA) and tositumomab radiolabeled with iodine-131 (Bexxar®, GlaxoSmithKline, UK), were approved for NHL treatment by FDA in 2002 and 2003, respectively.