Abstract
Rosai-Dorfman disease (RDD) is a rare myeloproliferative disorder of histiocytes. The cause of the disease remains unclear. RDD mainly affects lymph nodes and has many extranodal manifestations, including the skin, lungs, eyes, and gastrointestinal tract. This report details a diagnostically challenging case where retroperitoneal lymphadenopathy initially suspected as metastatic prostate adenocarcinoma was pathologically confirmed as RDD. The concurrent occurrence of these two distinct pathologies underscores the importance of histopathological verification in atypical presentations, particularly for guiding precision oncology management.