Cutaneous malignancies simulating seborrheic keratoses: An underappreciated phenomenon?

Seborrheic keratosis (SK), a common and benign entity, is generally diagnosed clinically without the need for a biopsy. Given their variable appearance, SK may mimic cancer clinically and require biopsy for clinically equivocal cases. A clinician may also choose to perform biopsies on SK based on other circumstances, such as cosmetic reasons or SK being in an inconvenient and irritative location.

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 and so on were excluded. A total of 4361 eligible cases were identified and used for analysis.

Of the 4361 cases identified as only "SK" or "ISK" in the clinical data, 3759 (86.2%) were, in fact, SK or ISK. A total of 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 (9/136 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.

SK may mimic cancer even in clinically unsuspicious cases.