Epithelioid angiosarcoma at chest wall which needs to be carefully distinguished from malignant mesothelioma: report of a rare case.

Angiosarcoma is a malignant soft tissue tumor the cells of which variably recapitulate the morphologic and functional features of normal endothelium. Most lesions are located in the deep muscles of the lower extremities followed by the arm, trunk and head and neck. Herein we present a case of epithelioid angiosarcoma which is a variant of angiosarcoma at chest wall in a 73-year-old female. Morphologically, the tumor cells are arranged predominantly in luminal structures which can be seen in both angiosarcoma and malignant mesothelioma. Most of the tumor cells are large rounded "epithelioid" cells with abundant eosinophilic cytoplasm which can be also seen in both tumors. The epithelioid of cytomorphology and the localization at chest wall of this case may remind of a diagnosis of malignant mesothelioma which should be carefully distinguished from epithelioid angiosarcoma from imaging and morphology. CT scanning of the patient shows a mass at her chest wall, the majority of which is around the rib but not inside the lung which indicates a tumor originates more likely from soft tissues of chest wall but not pleura. Immunohistochemical staining shows that the tumor cells are positive for cytokeratin, CD31, Vimentin and WT1, and negative for CEA, TTF-1, Calretinin, Mesothelial Cell (MC), CD56, CK19, and Hepatocyte. Thus this case is diagnosed as epithelioid angiosarcoma but not malignant mesothelioma. From this case we suggest that carefully reading and understanding of the imaging are a very important clue for appropriate diagnosis. A misdiagnosis may occur on the basis of misunderstanding of tumor localization and a consequent inappropriate immunohistochemical staining programme.