Primary gastrointestinal clear cell sarcoma: report of 2 cases, one case associated with IgG4-related sclerosing disease, and review of literature.

Clear cell sarcoma (CCS) is a distinctive soft tissue sarcoma that shows melanocytic differentiation. Primary gastrointestinal (GI) CCSs have been rarely reported, but to our knowledge, no association between GI CCSs and immunoglobulin G4 (IgG4)-related sclerosing disease has been described in the literature. We experienced 2 cases of CCS that arose in the small intestine and metastasized to the liver. Histologic features and immunophenotype were typical of CCS. One of them showed a unique peritumoral sclerosing inflammatory reaction, which was highly reminiscent of IgG4-related sclerosing inflammatory disease. Dense lymphoplasmacytic infiltration with extensive sclerosis and obliterative phlebitis was observed in the immediate vicinity of the primary and metastatic tumors, but not in the distant areas from the tumor. The average number of IgG4-positive plasma cells was more than 50 per high-power field. We report 2 cases of primary GI CCS with one case showing a unique peritumoral IgG4-related lymphoplasmacytic sclerosing inflammation.