Elastin: A Matter of Boundaries

Malignant melanomas (MMs) may arise de novo or associated with a melanocytic nevus; as many as 30% of MMs are of this second type. Evaluation of nevi-associated MMs is complicated by difficulties in distinguishing the boundaries between the nevus and the MM, but the need to determine Breslow thickness and tumor stage makes such distinction important. Because distinctive patterns of elastic fibers occur in nevi and MMs, these researchers evaluated the use of elastic-fiber staining in diagnosis.

In this retrospective study, researchers stained tissues from 30 patients with nevus-associated MMs, 12 control patients with melanocytic nevi, and 14 control patients with invasive melanomas. Staining was performed with the histochemical elastic van Gieson (EVG) stain and elastin immunostain. Elastin was superior for delineating the elastic fibers in the papillary and reticular dermis. In the control nevi and in the nevi component of the nevi-associated MMs, the elastic fibers were found between nests of melanocytes and around individual melanocytes. These elastic fibers were thicker, longer, and straighter than elastic fibers of uninvolved skin. In the control MM and in the invasive component of nevi-associated MM, elastic fibers were sparse or absent in the stroma and nests, and the melanoma pushed down and compressed the thin elastic fibers, forming a border between the nevus and the MM. In more than half the cases, the nevi were detected underneath the MM. An inflammatory response in the pigmented lesion obscured the pattern of staining.