Myofibroblastoma of the Chest Wall

Abstract

We describe a case of myofibroblastoma of the soft tissue of the chest wall occurring in a 5-year-old boy. The lesion consisted of a proliferation of monomorphous spindle-shaped cells with interspersed extracellular matrix, arranged in interlacing fascicles. Immunohistochemically, neoplastic cells showed a diffuse cytoplasmic staining for vimentin and actin and a strong surface positivity for fibronectin. Ultrastructurally, the cytoplasm of tumor cells contained abundant rough endoplasmic reticulum cisternae and peripheral bundles of microfilaments with focal densities. In addition, several fibronexus junctions were identified. The combination of these histomorpliologic and ultrastructural features indicates myofibroblastic differentiation of neoplastic cells. We hypothesize that soft-tissue myofibroblastoma may be related to infantile hemangiopericytoma and infantile myofibromatosis, representing the final maturative step in a spectrum of lesions formed by myofibroblasts and pericytes in the more immature variants and exclusively by myofibroblasts in the more mature lesions. Int J Surg Pathol 0(0):00-00, 1996