Synchronous histiocytic sarcoma and diffuse large B cell lymphoma involving the stomach: a case report and review of the literature.

We present a 62-year-old Chinese woman with histiocytic sarcoma (HS) and diffuse large B cell lymphoma (DLBL) located in the stomach. HS showed abundant eosinophilic cytoplasm with large, pleomorphic nuclei. Tumor giant and multinucleated cells were also prominent. Hemophagocytosis was common in the neoplastic cells. These cells were positive for CD68, CD45RO, and leukocyte common antigen (LCA), partly positive for S-100 and lysozyme, and negative for CD3, CD5, CD20, Pax-5, CD79a, CD1a, CD21, CD35, CD34, myeloperoxidase, HMB45 and cytokeratin (CK). These cells invaded the submucosa, muscularis mucosa, and serosa. DLBL was located in the mucosa and engulfed the covering epithelium and gland. The nuclei of tumor cells were medium-to-large in size, being ≥twice the size of normal lymphocytes. They were diffusely positive for CD20, Pax-5, and LCA, partly positive for vimentin, CD79a, CD10, CD30, CD15, and epithelial membrane antigen, and negative for S-100, CD1a, CD21, CD5, cyclin D1, CD23, CD35, HMB45, and CD68. Both types of tumor cell were positive for Oct-2, Bcl-2, and Bcl-6. These results suggest that HS may have shared a common clonal origin with DLBL, or may have transdifferentiated from DLBL The patient refused further chemotherapy, and died 7 months after surgical resection.