<b>Results:</b> IRF4/MUM1 expression was observed in 33% of all patients (23/69), most frequently in patients with anaplastic large cell lymphoma (ALCL, 78%, 7/9).
Among all cutaneous T-cell lymphoproliferative disorders, FISH for IRF4 had a specificity and positive predictive value for cutaneous anaplastic large cell lymphoma of 99 and 90%, respectively (P=0.00002, Fisher's exact test).