Interobserver variability on the histopathologic diagnosis of cutaneous melanoma and other pigmented skin lesions

PURPOSE: To assess the interobserver agreement on the diagnosis and classification of cutaneous melanoma. MATERIALS AND METHODS: A set of 140 slides of cutaneous melanoma, including a small subset of benign pigmented skin lesions, were circulated to four experienced histopathologists. The kappa statistic for multiple ratings per subject was calculated using the method described by Fleiss. RESULTS: The kappa value on the diagnosis of cutaneous melanoma versus benign lesions was 0.61. There was some discordance on the diagnosis in 37 of 140 cases (26%). For the histopathologic classification of cutaneous melanoma, the highest kappa values were attained for Breslow thickness (kappa = 0.76) and presence of ulceration (kappa = 0.87). The agreement was generally poor for other histologic features, such as level of dermal invasion (kappa = 0.38), presence of regression (kappa = 0.27), and lymphocytic infiltration (kappa = 0.27). CONCLUSION: Our study suggests considerable disagreement among pathologists on the diagnosis of melanoma versus other pigmented lesions. Tumor thickness and presence of ulceration are the most reproducible histologic features of cutaneous melanoma.