Histiocytic sarcoma with acute lymphoblastic leukemia a rare association: case report and literature review.

Definition and diagnostic criteria for histiocytic sarcoma (HS) have changed over last two decades due to available new immunohistochemical markers, as well as better understanding of the biology of disease. We report here a case of 4 years old boy diagnosed as acute lymphoblastic leukemia (ALL), who later developed HS of pleura, when he was on maintenance phase of ALL protocol. HS constitutes less than 1 % of the haematolymphoid neoplasm, even more rare is association of HS with ALL. Thus reporting here a rare association of HS with ALL, will help in knowing the actual incidence of HS as well as association with ALL.