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Cytokeratin-positive interstitial reticulum cell sarcoma: extranodal presentations mimicking carcinoma.

Cytokeratin-positive interstitial reticulum cell (CIRC) sarcoma is a rare type of dendritic cell tumor derived from a subset of fibroblastic reticular cells. Expression of cytokeratins and extranodal location of these tumors can lead to a misdiagnosis of carcinoma. We report two cases of CIRC sarcomas primarily involving the scalp and breast. Patients were referred with an initial diagnosis of carcinoma. Case 1 underwent wide local excision of the scalp tumor with left posterolateral neck dissection. Case 2 had modified radical mastectomy for the tumor in left breast. Histopathological examination of both specimens showed an epithelioid to spindle cell malignant tumor that co-expressed CK 8, CK 18, vimentin, and smooth muscle actin. A diagnosis of CIRC sarcoma was made. Pathologists should be aware of this subset of dendritic cell sarcoma. Carcinomas, other sarcomas of the accessory dendritic cell family, and poorly differentiated malignant tumors have to be ruled out by combination of morphology, immunohistochemistry, and electron microscopic studies.