Introduction and importance: Histiocytic sarcoma (HS) is a rare malignant neoplasm showing morphologic and immunohistochemical features of histiocytes. It is characterized typically by extranodal presentation and a poor clinical course, particularly in cases with disseminated disease.
Case presentation: This report documents a case of bifocal and aggressive HS in small bowel and lung revealed by acute peritonitis in a 63-year-old man.
Clinical discussion: Despite its rarity, we believe that the correct diagnosis of HS is crucial for clinical treatment and prognostic prediction.
Conclusion: The collection of additional cases of HS are important to obtain further progress in prognosis and guide treatment decisions.
Keywords: Acute peritonitis; Histiocytic sarcoma; Lung; Prognosis; Small intestine.
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