Dermoscopy of squamous cell carcinoma and keratoacanthoma.

OBJECTIVES To characterize dermoscopic criteria of squamous cell carcinoma (SCC) and keratoacanthoma and to compare them with other lesions. DESIGN Observer-masked study of consecutive lesions performed from March 1 through December 31, 2011. SETTING Primary care skin cancer practice in Brisbane, Australia. PARTICIPANTS A total of 186 patients with 206 lesions. MAIN OUTCOME MEASURES Sensitivity, specificity, predictive values, and odds ratios. RESULTS In a retrospective analysis of 60 invasive SCC and 43 keratoacanthoma cases, keratin, surface scale, blood spots, white structureless zones, white circles, and coiled vessels were commonly found in both types of lesions. We reevaluated the significance of these criteria in 206 raised, nonpigmented lesions (32 SCCs, 29 keratoacanthomas, and 145 other lesions). Central keratin was more common in keratoacanthoma than in SCC (51.2% vs 30.0%, P = .03). Keratin had the highest sensitivity for keratoacanthoma and SCC (79%), and white circles had the highest specificity (87%). When keratoacanthoma and SCC were contrasted with basal cell carcinoma, the positive predictive values of keratin and white circles were 92% and 89%, respectively. When SCC and keratoacanthoma were contrasted with actinic keratosis and Bowen disease, the positive predictive value of keratin was 50% and that of white circles was 92%. In a multivariate model, white circles, keratin, and blood spots were independent predictors of SCC and keratoacanthoma. White circles had the highest odds ratio in favor of SCC and keratoacanthoma. The interobserver agreement for white circles was good (0.55; 95% CI, 0.44-0.65). CONCLUSIONS White circles, keratin, and blood spots are useful clues to differentiate SCC and keratoacanthoma from other raised nonpigmented skin lesions by dermoscopy. The significance of these criteria depends on the clinical context.