Myofibroblasts and extracellular matrix glycoproteins in palmar fibromatosis.

We investigated immunohistochemically the presence of myofibroblasts and their surrounding extracellular matrix (ECM) in palmar fibromatosis nodules, obtained from 30 patients. Histologically, the three following phases were identified in palmar fibromatosis nodules: proliferative, involutional, and residual. A variable association of these phases was simultaneously detected within the same nodule. In most cases (20/30), we found that involutional and residual phases coexisted, while the association of proliferative/involutional/residual and proliferative/involutional phases was observed in 8 and 2 cases, respectively. Alpha-smooth muscle actin, a reliable marker for myofibroblastic cellular phenotype, revealed that most spindle-shaped cells of cellular areas of both proliferative and involutional phases were myofibroblasts. Regardless of the predominant association of histologic phases, these findings demonstrate that a myofibroblastic cellular component is constantly found in palmar fibromatosis nodules, although its degree is variable. Immunohistochemical study of ECM showed that collagen types IV, VI, laminin, and fibronectin were strongly expressed and restricted to cellular areas of involutional and residual phases. A combined study of cellular phenotype and ECM, using consecutive sections, demonstrated that the distritubion of collagen types IV, VI, laminin, and fibronectin followed the distribution of myofibroblasts, while they were not expressed in the areas devoid of these cells. These findings suggest that interactions between myofibroblasts and these surrounding ECM glycoproteins may be involved in the pathophysiology of palmar fibromatosis.