Background: Seborrheic keratoses (SK) are the most common cutaneous neoplasm in humans. Given their numbers, a squamous cell carcinoma in situ (SCCIS) arising from an SK would not be unexpected, although this occurrence has not been widely reported. Objective: This study compares the immune status of patients with a SCCIS arising contiguously from SK (SK/SCCIS) and the number of daily medications taken by these patients. The biopsy tissue was evaluated for the presence of human papillomavirus DNA. Methods: Over a 5-year period at our institution, 13 cases of SK/SCCIS were diagnosed. For each case, age- and sex-matched control patients with a histologically diagnosed unremarkable SK were randomly selected. The number of patients taking immunosuppressing medications was determined from each group and compared statistically. In addition, polymerase chain reaction analysis of the 13 SK/SCCIS biopsies was performed. Results: Five of the 13 study patients took immunosuppressive medications compared to none of the 39 control patients (P = 0.0005). None of the biopsies demonstrated the presence of human papillomavirus DNA by polymerase chain reaction. Conclusions: Immunocompromised patients with SKs appear to carry a greater risk of these otherwise innocuous lesions developing an SCCIS, although given the small number of patients evaluated, further research into this possible association is warranted.
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