Histologic parameters of melanoma deposits in sentinel lymph nodes (SLNs) have been shown to be predictive of the presence or absence of tumor in non-SLNs and clinical outcome, but assessment of these parameters is prone to inter-observer variation.

Histologic sections of 44 SLNs containing metastatic melanoma were examined by 7 pathologists. Parameters assessed included cross-sectional area of tumor deposits, cross-sectional area of SLNs, percentage of SLN area involved by tumor calculated from the two previous parameters, estimated percentage of SLN area involved by tumor, tumor penetrative depth (TPD), location of tumor within the SLN, and presence of extracapsular spread (ECS). Levels of inter-observer agreement were measured using intraclass correlation coefficients (ICC).

There was good to excellent inter-observer agreement on measurement of quantitative parameters: maximum size of largest tumor deposits, calculated area of 3 largest tumor deposits, percent area of SLN involved by tumor and TPD (ICC 0.88, 0.73, 0.68 and 0.83, respectively). There was moderate agreement on the evaluation of subcapsular versus non-subcapsular location of tumor deposits (ICC = 0.50). Agreement on assessment of ECS was fair (ICC = 0.39).

Assessment of some of the quantitative parameters was highly reproducible between pathologists. However, evaluation of the location of tumor deposits within SLNs and assessment of ECS was less reproducible. Clearer definitions and training can be expected to improve the reproducibility of assessment. These results have important implications for the reliability and reproducibility of these parameters in staging, prediction of outcome, and clinical management of melanoma patients.