Squamous cell carcinoma arising from lupus vulgaris on an old burn scar: diagnosis by polymerase chain reaction.

A 66-year-old Japanese woman with a squamous cell carcinoma (SCC) arising from lupus vulgaris (LV) on an old burn scar on the left lower extremity is described. Ziel-Neelsen stain of a direct smear from the surface exudate showed acid-fast bacilli. Repeated culture for tubercle bacilli was negative, probably due to a technical error. The diagnosis of LV was successfully made by polymerase chain reaction (PCR). LV and burn scar are common preceding diseases for SCC. The former is rare in the U.S., Europe, and Japan. We were unable to determine whether only one of the two conditions or a combination of both was the true predisposing factor responsible for the development of this SCC. However, this case may be the first report of SCC arising from coexistent LV and a burn scar in which the diagnosis was confirmed by PCR.