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Intranodal palisaded myofibroblastoma (IPM) is a rare benign spindle-cell tumor of lymph nodes with myofibroblastic/ smooth muscle differentiation. We present another case of IPM that confirms the myofibroblastic differentiation of the tumor cells and identifies the so-called amianthoid fibers as collagen deposits by immunohistochemical and ultrastructural techniques. Because IPM shares histomorphologic characteristics with an inflammatory myofibroblastic tumor that has been associated with a virus-induced alteration of cell cycle regulation, the diagnostic approach was extended in this case. We were able to demonstrate cyclin D1 overexpression but could detect neither amplification of the CCND1 gene nor allelic loss at chromosomes 9p22-21 and 13q (surrounding the genes p16 and Rb, respectively). Furthermore, no evidence of human herpesvirus-8 or Epstein-Barr virus infection could be found by polymerase chain reaction or immunostaining. Nevertheless, our results point to the cell cycle regulatory genes as a factor in the pathogenesis of IPM. [ABSTRACT FROM AUTHOR]