CD1A and sinus histiocytosis with massive lymphadenopathy: The authors can therefore determine whether the patient is RDD, IgG4-RD, or an overlap of the two through the IHC results of IgG, IgG4 and the ratio of IgG4/IgG plasma cells combined with the pathological manifestations and the staining results of s-100, CD68, and CD1a.