[Histiocytic sarcoma derived from the same origin as splenic marginal zone lymphoma revealed by exome analysis]

Histiocytic sarcoma (HS) is a rare aggressive hematological malignancy reported to occur secondary to B cell lymphoma. We report a case of HS secondary to splenic marginal zone lymphoma (SMZL) complicated by autoimmune hemolytic anemia (AIHA) in a 64-year-old man. He was referred to our department with anemia and was diagnosed as having AIHA. After starting treatment with prednisolone, atypical lymphocytes appeared in his blood tests, and a bone marrow biopsy revealed invasion by B cell lymphoma. A CT scan showed splenomegaly and a pancreatic mass, which confirmed the diagnosis of SMZL. The patient received bendamustine and rituximab as chemotherapy, which rapidly improved the anemia and splenomegaly and reduced atypical lymphocytes. However, left lumbar back pain appeared along with an increase in the pancreatic mass, and he died suddenly of acute renal failure. An autopsy revealed that the tumor had invaded several organs including the pancreas, and immunohistochemistry was positive for CD163, leading to the diagnosis of HS. Furthermore, the specimens of SMZL and HS were positive for IgH gene reconstitution, and exome analysis showed genetic abnormalities in 226 genes including CARD11, suggesting that the SMZL and HS had the same origin.