Interobserver and Intraobserver Agreement for the Laterally Spreading Tumor Classification in Large (>2 cm)...

Morphological assessment of large (≥20 mm) colorectal laterally spreading tumor (LSTs) is central to predicting submucosal invasion risk, procedural difficulty, and optimal resection strategy. The LST classification is widely used; however, its diagnostic reliability has never been formally evaluated.

We performed a prospective multicenter video-based study. Twenty-four blinded expert endoscopists from North America, Europe, Asia, and Oceania independently classified video-recorded LSTs twice, in randomized order, into 5 prespecified LST subtypes. Interobserver and intraobserver agreement were calculated using Light kappa. Secondary analyses evaluated agreement by LST size category, endoscopist sex, geographic training region, and a simplified 3-category granular vs nongranular classification.

Forty-six LSTs were evaluated, yielding 1,104 classifications. Interobserver agreement for the primary outcome was poor in both the first (κ = 0.37) and second assessment rounds (κ = 0.36). Agreement varied modestly across LST size groups and endoscopist characteristics, with moderate agreement in Europe and Oceania and fair agreement in North America and Asia. Simplifying morphology into 3 categories improved interobserver agreement to the moderate range (κ ≈ 0.48). Intraobserver agreement ranged widely (κ = 0.28-0.94), with the highest reproducibility among endoscopists trained in Europe and Oceania. Intraobserver agreement was generally higher for smaller lesions (<40 mm) and improved when using the 3-category model.

Among international experts, interobserver agreement for the LST classification is low, with considerable interobserver and intraobserver variability. These findings highlight the need for improved standardization and suggest caution when using detailed LST subclassification for clinical decision making or as an end point in research.