Evaluation of a new grading system for laryngeal squamous intraepithelial lesions--a proposed unified classification.

AIMS: To verify the applicability, reproducibility and predictive value of a proposed unified classification (amended Ljubljana classification) for laryngeal squamous intraepithelial lesions (SILs). METHODS AND RESULTS: Six internationally recognized experts and three pathologists from Ljubljana contributed to this study by evaluating a set of laryngeal SILs using the new system: low-grade SIL, high-grade SIL, and carcinoma in situ (CIS). The overall agreement among reviewers was good. Overall unweighted and weighted κ-values and 95% confidence intervals were 0.75 (0.65-0.84) and 0.80 (0.71-0.87), respectively. The results were stratified between the international reviewers and the Ljubljana pathologists. The former had good overall agreement, and the latter had very good agreement. Kaplan-Meier survival curves showed a significant difference (P < 0.0001) between patients with low-grade and high-grade SILs; 19 of 1204 patients with low-grade SILs and 30 of 240 patients with high-grade SILs progressed to malignancy in 2-15 years and in 2-26 years, respectively. CONCLUSIONS: The proposed modification to the Ljubljana classification provides clear morphological criteria for defining the prognostic groups. The criteria facilitate better interobserver agreement than previous systems, and the retrospective follow-up study demonstrates a highly significant difference in the risk of malignant progression between low-grade and high-grade SILs.