Intranodal palisaded myofibroblastoma expressing DOG1: focusing on the potential diagnostic pitfalls.

Intranodal palisaded myofibroblastoma (IPM) is a rare, benign mesenchymal neoplasm of the lymph nodes with a broad differential diagnosis. We report a case of an 82-year-old woman presenting with a slow growing, right inguinal mass. The tumor arose as a circumscribed neoplasm inside a lymph node and consisted of bland spindle cells with nuclear palisading and intervening areas of amianthoid-like fibers among interstitial hemorrhage and hemosiderin-laden histiocytes in the stroma, typical histomorphological characteristics of IPM. Immunohistochemically, the neoplastic cells were positive for vimentin, smooth muscle actin (SMA), β-catenin, cyclin D1 and discovered on gastrointestinal stromal tumor (GIST) 1 (DOG1) immunostainings. A literature review and differential diagnosis of IPM are discussed. To the best of our knowledge, this is the first case of DOG1 immunoexpression in a case of IPM.