Interobserver agreement in the histopathological classification of desmoplastic melanomas

Desmoplastic melanoma is a subtype of melanoma char-acterised by amelanotic fusiform melanocytes dispersed in a collagenous stroma. Cell-poor and fibrous stroma-rich 'pure' variants have been distinguished from 'mixed' vari-ants with areas of higher cell density and/or less desmo-plastic stroma. This distinction is relevant because patients whose tumours display a pure phenotype have a lower risk for regional lymph node metastasis and distant recurrence. However, little is known about interobserver agreement among pathologists in the subclassification of desmo-plastic melanoma. To address this issue, we conducted a study in which eleven dermatopathologists independently evaluated whole slide scanned images of excisions from 30 desmoplastic melanomas. The participating patholo-gists were asked to classify the tumours as pure or mixed. They were also asked to record the presence or absence of neurotropism and angiotropism. We found substantial interobserver agreement between the 11 dermatopathol-ogists in the classification of tumours as pure versus mixed desmoplastic melanoma (kappa=0.64; p<0.0001). There was fair agreement between the 11 dermatopathologists in the evaluation of presence versus absence of neuro-tropism (kappa=0.26; p<0.0001), and slight agreement in the assessment of angiotropism (kappa=0.13; p<0.0001). The level of concordance in the subclassification of desmoplastic melanomas is encouraging for the accep-tance of this prognostic parameter in the real-world prac-tice of melanoma pathology.

Automated summary

Desmoplastic melanoma can be classified into pure and mixed types based on morphological characteristics, which have different risks of lymph node metastasis and distant recurrence. A study showed a substantial interobserver agreement among dermatopathologists in the classification of desmoplastic melanoma, indicating the potential clinical application of this classification as a prognostic factor in melanoma pathology.