IRF4 and Lymphomatoid Papulosis: Chromosomal rearrangements involving the DUSP22-IRF4 (MUM1) locus on 6p25.3 have also been identified in both pcCD30+ ALCL (25%) and less commonly (5%) in lymphomatoid papulosis (LYP) (69), but MUM1 expression is not specific for this rearrangement.