Histiocytic Sarcoma of the Eyelid: An Uncommon Presentation of a Rare Neoplasm.

Histiocytic sarcoma is an extremely rare malignancy typically presenting in extranodal sites, including the gastrointestinal tract, lung, nasal cavity, and soft tissue. Primary presentation in the skin is an even rarer entity, with only one prior case reported in the eyelid skin. Herein, we describe a case of histiocytic sarcoma that presented in the eyelid of an 80-year-old man. The lesion presented as a rapidly growing left lower eyelid lesion over 4 months. Shave biopsy revealed histologic and immunophenotypic findings most consistent with a morphologically low-grade histiocytic sarcoma. Complete excision was performed with an additional 2 mm peripheral and deep margins, which were found to be clear of malignancy. Systemic work-up and whole body imaging showed no evidence of metastases or other associated malignancy. The decision was made to forego radiation and proceed with close observation every 3 months. Two years from presentation, the patient had no evidence of recurrence.