Extranodal histiocytic sarcoma in a child with acute lymphoblastic leukemia: Cytomorphological features of a rare entity with brief review of literature.

Histiocytic sarcoma (HS) is a rare malignant neoplasm showing morphologic and immunophenotypic evidence of histiocytic differentiation. We describe a rare case of synchronous HS in a patient of B-cell acute lymphoblastic leukemia (ALL). A 16-year-old boy diagnosed as ALL also presented with a swelling over the right Achilles tendon. The cytological features of the swelling suggested a histiocytic lesion. Histological and immunohistochemical examination clinched the diagnosis of HS. The available 5-year follow-up showed no recurrence. It was a diagnostic dilemma on fine-needle aspiration. We discuss the cytological features of HS which can help in reaching a diagnosis and emphasize that it should be considered in the differential diagnosis for unexplained swellings in patients of hematological malignancies. Wide local excision of localized HS is associated with a long-term favorable outcome.