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Case Reports

Abstract

Primary cutaneous extra-skeletal osteosarcoma (PCEOS) is an exceptionally rare and aggressive high-grade sarcoma with 25% metastatic rate, that produces malignant osteoid and does not involve the underlying bone.  The clinicopathologic characteristics and behavior is not fully elucidated. We present a case in a 73-year-old female with a history of type 2 diabetes mellitus and stage 4 chronic kidney disease who was referred to our orthopedic oncology clinic with a differential diagnosis of undifferentiated pleomorphic sarcoma / pleomorphic dermal sarcoma of the left lower leg. Imaging identified a calcified soft tissue mass involving the pretibial region with adjacent more confluent soft tissue thickening and edema along the lateral margin of the lesion. She received preoperative radiation therapy and underwent left below the knee amputation. On gross examination, the lesion appeared extra-skeletal in nature and measured 6.5 cm in greatest dimension. Sections demonstrate a high-grade spindled to epithelioid cell malignant neoplasm involving the dermis and subcutaneous fat. The underlying bone was not involved by the tumor. The tumor demonstrated marked pleomorphism with sheet-like growth pattern and osteoblastic, fibroblastic, chondroblastic, and giant cell areas. There were foci with lace-like malignant osteoid and bone formation by the neoplastic cells. Numerous mitosis and focal necrosis was present. SATB2 immunohistochemistry was diffusely positive in the tumor cells. S100 and pan-keratin were negative. PCEOS with negative surgical margins was diagnosed. The patient is doing well on 6 months follow up without any recurrence or metastasis.