Clear cell sarcoma of soft tissue with plasmacytoid morphology: A rare case report.

RATIONALE: Clear cell sarcoma of soft tissue (CCSST) is a rare malignant tumor that occurs in the extremities of young adults. CCSST has been documented to have atypical histopathological features, such as epidermotropism or myxoid differentiation, which may set pitfalls in the differential diagnosis. We report a case of CCSST with plasmacytoid morphology which has never been described. PATIENT CONCERNS: A 15-year-old male, presented with a 5-cm mass in his left inguinal area. DIAGNOSIS: Positron emission tomography-computed tomography examination showed nodules in the left groin and the lung, the latter was considered metastasis. A core needle biopsy with the diagnosis of CCSST with plasmacytoid morphology was made according to histology, immunostaining, and molecular analysis. INTERVENTIONS: The patient received chemotherapy of doxorubicin and ifosfamide. OUTCOMES: The patient failed to respond to the standard chemotherapy and deceased twelve months after diagnosis. LESSONS: This special case of CCSST with plasmacytoid features demonstrated a morphological variation never been documented and may easily lead to misdiagnosis. For such cases, molecular analysis is essential to provide solid evidence for accurate diagnosis.