Seborrheic keratosis (SK), a common and benign entity, may mimic cancer even in clinically unsuspicious cases, a recent study found. Dermatopathology samples from 2015 obtained from private and university locations were retrospectively assessed. Cases included in the study were those with “SK” or “ISK” (irritated seborrheic keratosis) and no other diagnosis in the clinical data. Cases with modifiers suggestive of malignancy such as “SK rule out others,” changing, growing, et cetera, were excluded. A total of 4,361 eligible cases were identified and used for analysis. Researchers found:

• Of total cases identified as only “SK” or “ISK” in the clinical data, 3,759 (86.2%) were, in fact, SK or ISK.
• 466 (10.7%) were an assortment of non-malignancy diagnoses such as dermatofibroma.
• There were 136 (3.1%) cases histologically diagnosed as malignancies.
• The majority (91/136 cases; 67%) were in situ or invasive squamous cell carcinoma, 24.3% (33/136) were basal cell carcinoma, and 8.8% (12/136) were melanoma.