Inflammatory monomorphic undifferentiated sarcoma with distinct clinical and pathological features: a ‘new’ entity?

Summary Aim To describe two patients with a highly aggressive, apparently ‘new’ and rare soft tissue and bone malig-nancy of childhood and early adult life that we have named inflammatory monomorphic undifferentiated sarcoma. Methods and results Two histologically identical tumours located in the proximal humerus and the anterior chest wall of males aged 6 and 31 presented as solitary, painful, tender, necrotising, masses, associated with fever, leukocytosis and negative microbiological cultures. The extensively necrotic resected tumours consisted of large, monomorphic epithelioid cells with vesicular nuclei, prominent eosinophilic nucleoli, and abundant eosinophilic cytoplasm surrounded by numerous neutrophils and eosinophils which formed sterile microabscesses. Immunohistochemical and ultrastructural studies revealed no specific differentiation. Both tumours were very aggressive, with early local recurrence, metastasis to regional and distant lymph nodes and viscera, and no response to several different chemotherapeutic regimens. Conclusion A careful review of the literature led us to believe that inflammatory monomorphic undifferentiated sarcoma may represent a rare and distinct clinico- pathological entity that does not appear to have been previously described.