Elastic fiber pattern in regressing melanoma: a histochemical and immunohistochemical study

Abstract

Although histopathologic identification of regression of melanoma is usually straightforward, sometimes it can be difficult to distinguish it from scarring fibrosis. Therefore, this study investigates the elastic fiber pattern in melanomas associated with either regression or scars. We compared 33 invasive melanomas with the fibrosing stage of regression to 10 cases of invasive melanomas with scarring fibrosis. None of the regression cases had a prior surgical procedure. Elastic fiber patterns were evaluated with Verhoeff's elastic van Gieson stain (EVG) and elastin immunostain. Elastin immunostain was superior to EVG in revealing the elastic fiber patterns. Both regression and scars had decreased to absent elastic fibers in the areas of fibrosis. However, areas of regression had a well-defined compressed layer of thin elastic fibers pushed down from the papillary dermis to the base of the fibrosis. In contrast, the base of scars lacked this compressed elastic layer and had instead an abrupt transition to the thick elastic fibers of the spared reticular dermis. We have identified distinct changes of the elastic tissue network, which more accurately define the presence of regression in melanoma and distinguish it from scarring fibrosis.