Primary Cutaneous Myxofibrosarcoma Mimicking Pleomorphic Hyalinizing Angiectatic Tumor (PHAT): A Potential Diagnostic Pitfall

Myxofibrosarcoma (MFS) is one of the most common sarcomas of adults, and includes lesions ranging from low to high grade based on increasing cellularity, nuclear pleomorphism, and mitotic activity. We present an unusual case of MFS, which initially showed features of a pleomorphic hyalinizing angiectatic tumor (PHAT), a rare soft-tissue tumor considered benign in the WHO classification. The initial lesion showed a subcutaneous proliferation of spindled to polygonal eosinophilic cells with striking cellular pleomorphism, set in a myxoid to sclerotic stroma with prominent hyalinized and angiectatic vasculature, classic characteristics of PHAT. Rare mitotic figures were identified. The preliminary diagnosis of PHAT was confirmed by a consultant expert soft-tissue pathologist. Four months after the initial surgery, local recurrence was noted. The recurrent tumor demonstrated findings of a high-grade MFS, with a diffuse and cellular proliferation of atypical spindle cells set in a prominent myxoid stroma. Multiple mitoses, including atypical ones, were present. In light of these findings, the original specimen was reexamined and the initial diagnosis was amended to MFS. MFS may mimic or be confused with several benign soft-tissue lesions. Cases mimicking PHAT have not been previously reported. We describe a unique case of a high-grade MFS that initially showed characteristic features of a PHAT, to illuminate the fact that MFS may rarely arise in, or have areas that masquerade as, PHAT. It is also conceivable, although speculative, that at least some cases of PHAT, currently considered a benign tumor by the WHO, may actually represent or evolve into a unique form of MFS of low malignant potential.