Histologic classification of tumor-infiltrating lymphocytes in primary cutaneous malignant melanoma - A study of interobserver agreement

The density and distribution of lymphocytes infiltrating the vertical growt h phase of primary cutaneous melanomas has been suggested by several studie s to be of prognostic significance. However few pathologists comment on tum or-infiltrating lymphocytes (TILs), and there is the perception that the as sessment of TILs is subject to great interobserver variability. We studied interobserver agreement on the categorization of TILs; 20 cases of primary cutaneous malignant melanoma with a vertical growth phase component were ci rculated among 3 pathologists and 3 dermatologists. For each case, TILs wer e classified as brisk, nonbrisk, or absent according to Clark. Only I patho logist (a dermatopathologist) was familiar with the classification of TILs. Observers were given written guidelines and a brief tutorial before their examination of the slides. Our results show that with little instruction, o verall agreement among observers was good (kappa values, 0.6 or more), espe cially among pathologists (kappa values, > 0.7). Three observers had excell ent agreement among each other (kappa values, > 0.75). These findings sugge st that the categorization of TILs can be easily taught and can be applied with an acceptable level of reproducibility in routine diagnostic practice.