Recurrent Soft Tissue Rosai Dorfman Disease of Right Medial Thigh Lipoma With Lymph Node Involvement.

Background: Rosai Dorfman disease is a rare non-Langerhans cell histiocytosis that affects lymph nodes, soft tissues, and other organs. The etiology of Rosai Dorfman disease is poorly understood, though it may involve an immunologic processes or infection. Treatment varies according to the disease presentation. Case Presentation: A male aged 56 years was evaluated for a cutaneous mass on his right medial thigh. Initially, the patient received surgical debulking with subsequent observation and no systemic therapy. However, the mass recurred, prompting another surgical removal 9 years after the initial surgery. A mass biopsy showed infiltration of plasma cells, lymphocytes, histiocytes, and occasional neutrophils with noted reactivity of S-100 protein and CD163, but not CD1a. No systemic therapy was initiated, and the patient agreed to a period of watchful waiting. Conclusions: Rosai Dorfman disease of soft tissue occurs in older adults and is often associated with soft tissue abnormalities, and more rarely, in lipomas. Multidisciplinary management of the disease and research for mutations and microenvironment of RDD is needed to better understand its clinicopathological nature and improve novel therapies.