Intrapelvic Bulky Tumor as an Unusual Presentation of Erdheim-Chester Disease.

Erdheim-Chester disease (ECD) is a rare form of non-Langerhans cell histiocytosis, which is known to affect various organs; however, there have been no reports of its intrapelvic involvement. We herein describe the case of 69-year-old man who died of a rapidly-growing intrapelvic tumor, which was finally diagnosed as ECD at autopsy. Immunohistochemically, the tumor cells were positive for CD68 and BRAF V600E, and negative for CD1a. Since BRAF V600E has recently been reported to be specific to ECD, it can be a useful biomarker for diagnosis, especially in atypical cases.