Undifferentiated pleomorphic sarcoma requires adequate tissue sampling and comprehensive immunohistochemical evaluation to distinguish it from morphologically similar cutaneous tumors like atypical fibroxanthoma.
Background: Undifferentiated pleomorphic sarcoma is a rare and highly aggressive mesenchymal tumor that lacks a specific line of differentiation. Its clinical presentation is nonspecific, and it is frequently misdiagnosed as other fibrohistiocytic tumors such as atypical fibroxanthoma, leading to delayed definitive treatment. Case presentation: A 46-year-old female presented with a slowly enlarging mass on the right lower leg that had persisted for one year following a mosquito bite. Initial outpatient incisional biopsy with histopathological and immunohistochemical evaluation suggested atypical fibroxanthoma. The patient subsequently underwent wide local excision with flap reconstruction. Postoperative histopathological examination revealed a 5cm tumor exhibiting marked pleomorphism, and comprehensive immunohistochemical profiling confirmed the diagnosis of undifferentiated pleomorphic sarcoma. Unfortunately, surgical margins were positive at the superior and medial aspects. Although postoperative imaging showed no definitive residual tumor, and supplementary immunohistochemistry demonstrated positive vascular endothelial markers with no evidence of intravascular tumor emboli-indicating a favorable prognostic feature-this finding nonetheless provoked significant patient anxiety. The patient was subsequently referred to a tertiary care center for further wide re-excision and adjuvant chemoradiotherapy. Conclusion: Undifferentiated pleomorphic sarcoma remains a diagnosis of exclusion that requires adequate tissue sampling and comprehensive immunohistochemical evaluation to distinguish it from morphologically similar cutaneous tumors such as atypical fibroxanthoma. A high index of suspicion should be maintained for large, deep-seated, or rapidly growing fibrohistiocytic lesions, and biopsies should procure sufficient depth and breadth to avoid misdiagnosis. Early and accurate diagnosis is critical for achieving complete resection, alleviating patient anxiety, and improving prognosis.
Wang et al. (2026) studied this question.