Rare mimic of a myxofibrosarcoma: cutaneous myxoid spindle cell squamous cell carcinoma as a complication of chronic osteomyelitis

Myxoid spindle cell squamous cell carcinoma is a rare variant of squamous cell carcinoma that can pose diagnostic challenges because of its unusual morphology. In this article, we report the case of a 68-year-old man who presented with a slow-growing, fungating mass on the right tibia at the site of his long-standing draining sinus tract. Biopsy revealed a malignant spindle cell tumor with prominent myxoid stroma and areas containing thin-walled blood vessels with a curvilinear appearance. The immunohistochemical profile indicated that the neoplastic cells were positive for a variety of keratins (MNF116, Cam 5.2, AE1/AE3, 34βE12, and CK5/6) and transcriptional markers classically expressed in squamous cell carcinomas (p63 and p40). The tumor cells were negative for melanocytic and mesenchymal markers smooth muscle antibody, S100, caldesmon-h, desmin and CD34. Together, the clinical history, histologic appearance, and immunohistochemical panel was diagnostic of a myxoid spindle cell squamous cell carcinoma. The main differential diagnosis was myxofibrosarcoma. In addition to this clinical case, we also outline the current state of knowledge on this rare entity and discuss the importance of recognizing a Marjolin ulcer in this scenario.