Interobserver reproducibility of histological features in cutaneous malignant melanoma

Aims: To assess the interobserver reproducibility of certain histological features proposed for the diagnosis of melanoma. Methods: In a series of melanomas, 13 histological parameters were analysed: dimension > 6 mm, asymmetry, poor circumscription, irregular confluent nests, single melanocytes predominating, absence of maturation, suprabasal melanocytes, asymmetrical melanin, melanin in deep cells, cytological atypia, mitoses, dermal lymphocytic infiltrate, and necrosis. Results: The agreement (reproducibility) between the nine observers was excellent (κ > 0.75) for 10 of the 13 examined features (dimension > 6 mm, poor circumscription, irregular confluent nests, single melanocytes predominating, absence of maturation, suprabasal melanocytes, asymmetrical melanin, melanin in deep cells, mitoses, and necrosis). The agreement for asymmetry was very close to excellence (κ = 0.74), and that for cytological atypia (κ = 0.65) and dermal lymphocytic infiltrate (κ = 0.47) was slightly lower, but in the fair to good agreement range. The κ values obtained by comparison with the majority diagnosis were generally high (≥ 0.85); the mean value of κ was lower (0.70) for only one parameter (dermal lymphocytic infiltrate). Conclusions: The parameters investigated showed an overall good reproducibility.