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.