Cytoskeletal characteristics of myofibroblasts in benign neoplastic and reactive fibroblastic lesions.

The characteristics of the cytoskeleton of myofibroblasts were examined immunohistochemically in 10 extra-abdominal desmoid tumours, 3 palmar and 2 plantar fibromatoses and 5 nodular fasciitis; in the cultured cells of one desmoid tumour, and also ultrastructurally in 3 desmoid tumours. Polyclonal anti-desmin antibody reacted with the cells in 7 extra-abdominal desmoid tumours, 1 palmar fibromatosis, 1 plantar fibromatosis and 3 nodular fasciitis. Monoclonal antidesmin antibody reacted with cells in only 2 desmoid tumours. Desmin-positive spindle cells were scattered throughout these lesions. There were no marked ultrastructural differences between desmin-positive and desmin-negative desmoids. All specimens except one specimen of nodular fasciitis showed immunoreactivity for alpha-smooth muscle actin and vimentin. Muscle actin-positive cells were observed in all specimens. Cultured cells gave positive reactions with polyclonal desmin antibody as well as to vimentin antibodies and two preparations of actin antibodies, whereas the original tumour did not react with desmin antibody. The present studies suggested that the cytoskeleton of some myofibroblasts in both neoplastic and reactive lesions resembles that of smooth muscle cells.