Histiocytic Sarcoma Arising From Pediatric Rosai Dorfman Disease: Two Novel Cases and Literature Review.

Rosai-Dorfman Disease (RDD) is an uncommon histiocytic disorder that can affect lymph nodes and/or extranodal sites. It is marked by the accumulation of abnormal histiocytes that demonstrate emperipolesis-the active, non-destructive engulfment of other leukocytes. RDD exhibits considerable variability in clinical presentation, pathology, genetics, treatment response, and patient outcomes. In this report, we describe 2 rare cases of RDD that underwent sarcomatous transformation and harbored MAP2K1 mutations, both of which demonstrated poor responses to multiple lines of therapy. Additionally, we review 3 other similar cases from the literature.