CD1A and sinus histiocytosis with massive lymphadenopathy: In the 2016 revised classification of histiocytoses, Rosai-Dorfman disease (RDD, also known as massive lymphadenopathy with sinus histiocytosis), was placed in the “R” group, which can be distinguished from “L” group (Langerhans) based on the absence of CD1a and CD207 expression.