Osteoclast-rich tumor of the gastrointestinal tract with features resembling those of clear cell sarcoma of soft parts.

Clear cell sarcoma is a high-grade sarcoma with morphological features resembling those of malignant melanoma. An osteoclast-rich tumor of the gastrointestinal tract with features resembling those of clear cell sarcomas of soft parts is very rare. Herein, we report an unusual stomach tumor with microscopic and immunohistochemical characteristics of an osteoclast-rich tumor of the gastrointestinal tract with features resembling those of clear cell sarcomas of soft parts. The tumor cells were predominantly oval, admixed with some round and spindle elements arranged in nests and fascicles, and admixed with scattered osteoclast-like multinucleated giant cells. Neoplastic cells were positive for S-100 protein, and osteoclast-like multinucleated giant cells were immunoreactive to CD68. The unusual morphology of the tumor caused significant diagnostic difficulties. The differential diagnosis included gastrointestinal stromal tumor, primary or metastatic melanoma, and epithelioid malignant peripheral nerve sheath tumor. To the best of our knowledge, this is possibly the second description of an osteoclast-rich tumor of the gastrointestinal tract with features resembling those of clear cell sarcomas of soft parts.