Metastatic small cell carcinoma of the lung with prominent spindle cell morphology and hemangiopericytoma-like vascular pattern: A sarcoma mimicker.

Small cell carcinoma is a malignant neuroendocrine tumor with aggressive clinical behavior. Histologically, the tumor is characterized by the proliferation of small, round, blue cells. Here, we present the case of a 50-year-old man with a 1-month history of enlarging chest wall mass. Microscopic examination of the lesion revealed a highly cellular neoplasm composed of closely packed, atypical spindle cells with scant cytoplasm, inconspicuous nucleoli, and brisk mitotic activity. The hemangiopericytoma-like vascular pattern was prominent. Areas showing a fibrosarcoma-like fascicular pattern were also observed. The tumor was immunohistochemically positive for TTF1, synaptophysin, and chromogranin, confirming small cell carcinoma. Further investigations revealed a lung origin and widespread metastases. The tumor in this case closely mimicked synovial sarcoma or malignant peripheral nerve sheath tumor. Small cell carcinoma demonstrates a hemangiopericytoma-like pattern that can mimic sarcoma histologically. This is a serious pitfall that can significantly affect the speed of diagnosis and management.