Ferruginous foreign body: a clinical simulant of melanoma with distinctive histologic features

A 53-year-old man reported a pigmented lesion on his forearm that he had first become aware of approximately 30 years previously. More recently, the lesion had become symptomatic and was excised because of concern of melanoma; however, during tissue processing, an embedded metallic object was found. Histologic examination of the tissue surrounding the site of the metallic object confirmed an inner zone of iron deposition with a distinctive histologic appearance indistinguishable from rust, associated with a foreign body reaction. Surrounding this was an outer zone of siderophages with the more usual histologic appearance. Chemical analysis of the foreign body confirmed its ferruginous nature. On subsequent questioning, the patient informed us that he had worked with heavy equipment in a mine at the time that he had first noticed the lesion.