Histiocytic sarcoma combined with acute monocytic leukemia: a case report

BACKGROUND Histiocytic sarcoma (HS) is a rare malignant tumor. Underlying or associated disorders have been reported in some patients with HS. We herein report a very rare case of HS combined with acute monocytic leukemia (AMoL). CASE PRESENTATION A 62-year-old man presented with systemic lymph node enlargement and pancytopenia in August 2012. Bone marrow (BM) aspirate showed abnormal hematopoiesis with 3% blast, but no obvious abnormalities on flow cytometric immunophenotyping. A BM cytogenetic study and fluorescence in situ hybridization revealed a 46, XY karyotype and no myelodysplastic syndrome-associated features, respectively. A right cervical node biopsy showed disrupted node structure with diffuse pleomorphic neoplastic cells that were positive for cluster of differentiation (CD) 68, MAC387 and lysozyme, but negative for CD1a, CD21, CD30, S100, and T-cell, B-cell, and myeloid lineage markers. The patient was diagnosed with HS and treated with 8 courses of CHOP chemotherapy. After 4 courses, total-body FDG-PET imaging showed partial remission and disappearance of abnormal hematopoiesis in the BM, but 2% blasts remained. Lymphadenopathy and pancytopenia recurred 1 month after the his last chemotherapy dose. He became resistant to second-line chemotherapy, with gradually increasing leukocytes, up to 50% blasts in BM in December 2013, and abnormal cells positive for CD117, CD13, CD33, HLA-DR, CD34, CD11c, CD38, and myeloperoxidase. He was diagnosed with acute monocytic leukemia (AMoL-M5), and treated by CAG regimen + decitabine, but died of severe pneumonia and hepatic failure. CONCLUSION To our knowledge, this is the first case of HS combined with AMoL. The coexistence of these two neoplasms was shown by the lymph node biopsy findings and BM myeloid markers. The patient had a transient response to chemotherapy and a poor prognosis. Whether these two neoplasms were related is unclear; however, if so, we suspect the combination might be caused by a malignant transformation of a promonocyte or stem cell, upstream of histiocytes and monocytes.