Transdifferentiation of Hairy Cell Leukemia to Lytic and Mass-Producing Histiocytic Sarcoma: A Novel Head and Neck Example and Review of the Literature.

BACKGROUND

Transdifferentiation of hairy cell leukemia to histiocytic sarcoma (HS) has not been previously reported in the head and neck. Given the rarity of HS, it can pose a challenge to diagnose this aggressive malignancy.

CASE PRESENTATION: A 93-year-old male with a complex medical history presented with symptomatic and mobile lower anterior teeth. No intraoral growth mass was present initially and radiographic examination showed a radiolucent lesion in the anterior mandible. An incisional biopsy under local anesthesia was performed and histopathologic examination revealed a malignant sarcoma which upon further clinical, immunohistochemical, and molecular workup, confirmed the diagnosis.

DIAGNOSIS: Initial histopathologic evaluation of the biopsy rendered a provisional diagnosis of undifferentiated pleomorphic sarcoma. The case was referred to a tertiary care center for complete medical workup and additional ancillary studies where it was definitively diagnosed as a HS. The patient passed away a month after this HS diagnosis.