GATA ‐3 expression in a de‐differentiated chondrosarcoma with cutaneous iatrogenic implantation: a diagnostic pitfall with important clinical implications

Abstract De‐differentiated chondrosarcoma (DDCS) is an extremely aggressive tumor of the bone characterized by a high‐grade, non‐chondroid sarcoma adjacent to a low‐ or intermediate‐grade chondrosarcoma. Adequate tumor sampling demonstrating the biphasic features is necessary to make an accurate diagnosis. The diagnosis may be challenging as histopathology may mimic other neoplasms. We present a case of a 76‐year‐old woman with a history of breast cancer who presented with a pathologic non‐displaced fracture. A bone biopsy demonstrated a high‐grade neoplasm composed of pleomorphic spindled and epithelioid cells with focal expression of AE1/3 and GATA3, most likely consistent with metastatic breast carcinoma. After a difficult clinical course, the tumor was resected demonstrating a similar morphology to her prior biopsy, as well as an area of a low‐grade cartilaginous neoplasm consistent with chondrosarcoma. The biphasic tumor alongside a low‐grade chondrosarcoma allowed for a diagnosis of DDCS. Several days after her procedure, the patient developed violaceous nodules overlying and surrounding the surgical site. Skin biopsy demonstrated a malignant epithelioid neoplasm with identical histomorphologic features identical to her prior bone resection. Given the location of the skin lesions directly within the surgical site right after resection, the clinical‐pathological picture was that of sarcomatosis cutis by iatrogenic cutaneous implantation.