Background: Seborrheic keratoses (SKs) may sometimes mimic benign and malignant skin tumors, and a biopsy can be necessary in order to rule out malignancy. Methods: From the database of our pigmented lesion clinic, we evaluated the dermoscopic features of difficult-to-diagnose SKs that were biopsied between January 2010 and December 2014. Results: SKs represented 3.8% of all excised lesions (161/ 4,182). Specifically, 91 (56.5%) were excised to rule out melanoma, 63 (39.1%) to rule out squamous cell carcinoma and 7 (4.4%) to rule out basal cell carcinoma. The following 10 global dermoscopic patterns were identified: multicomponent (32; 19.9%); reticular (24; 14.9%), characterized by an irregular pigment network; bowenoid (21; 13.0%); hairpin (19; 11.8%); keratoacanthoma-like (16; 9.9%); blue-nevus-like (15; 9.3%); lichenoid (6; 3.7%); hyperkeratotic (6; 3.7%); clonal (5; 3.1%); spitzoid (5; 3.1%). Furthermore, 12 SKs (7.5%) were not included in any of such patterns (not classified). Conclusion: Our results are in line with previous studies highlighting the dermoscopic variability of SKs. Although excised SKs may be classified into 1 of 10 repetitive dermoscopic patterns, a biopsy remains mandatory for those that cannot be clearly differentiated from common skin malignancies.

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