Abstract
Seborrheic keratosis (SK) is a common epidermal tumor generally regarded as benign. One histopathologic variant, SK with clonal pattern (cSK), displays histologic features distinct from typical SKs. We sought to quantitatively assess the risk of recurrence and progression to squamous cell carcinoma (SCC), either in-situ, or invasive, in a large-scale review of cases diagnosed as cSK or intraepidermal epithelioma (equivalent term). We queried our computer pathology data management system for the terms “seborrheic keratosis, clonal pattern” and “intraepidermal epithelioma” over a period of 10 years (2008-2018). Demographic, clinical, pathologic and follow-up data were gleaned from electronic health records. Cases with overlapping, equivocal, irrelevant, or initially malignant diagnoses were excluded. Following glass slide review, lesions were divided into two groups: CSK with atypia and CSK without atypia. The minimum follow-up interval was 2 years (median = 4 years). 243 unique cases of cSK fulfilled criteria for the stuidy. All were were incompletely excised by the initial biopsy. Eighteen (7%) recurred at or adjacent to the site of initial partial removal, 5 of which recurred as cSK, 10 as SCC in-situ, and 3 as invasive SCC. The mean time to recurrence was 4 years. Atypia in original specimen was not associated with recurrence risk. Clonal-pattern seborrheic keratoses recur at the site of incomplete excision at a rate of 7%. Importantly, in this study 5 % recurred as in-situ or invasive squamous cell carcinoma. Our results suggest that close clinical follow-up of cSK is warranted. Further studies characterizing the pathologic and molecular features of cSK associated with recurrence and upgrade to carcinoma are needed.Financial Disclosure: No current or relevant financial relationships exist.