Diagnostic Performance and Reproducibility of Chromoendoscopic Classification (FOCUS Classification: Flat-Type Dysplasia Optical Assessment by Chromoendoscopy in Ulcerative ColitiS) for Flat-Type Dysplasia in Ulcerative Colitis-Associated Neoplasia.

OBJECTIVES: Ulcerative colitis-associated neoplasia (UCAN) often presents as flat-type dysplasia that is difficult to characterize endoscopically. We developed a FOCUS (Flat-type dysplasia Optical assessment by Chromoendoscopy in Ulcerative colitiS) classification and evaluated its diagnostic performance and reproducibility. METHODS: This single-center retrospective study included 33 UCAN lesions from 26 patients. Prospectively recorded FOCUS classifications at 230 biopsy sites were compared with histopathology. Chromoendoscopic patterns were categorized as Type I ("suggestive of non-dysplasia,"), Type II ("suggestive of dysplasia with low confidence"), or Type III ("suggestive of dysplasia with high confidence"). Diagnostic performance was assessed using two prespecified thresholds: Types II/III versus Type I and Type III versus Types I/II. Eight endoscopists independently classified all images; interobserver and intraobserver agreement were assessed using Fleiss' and Cohen's κ, respectively. RESULTS: The dysplasia-bearing rate increased stepwise from Type I to Type III (Type I 15.5%, Type II 58.3%, Type III 81.8%). Using the primary threshold, sensitivity was 82.0%, and specificity 75.4% (positive likelihood ratio 3.33; negative likelihood ratio 0.24). Interobserver agreement for the three-category classification was moderate to substantial (Fleiss' κ 0.629; 95% CI 0.545-0.712), and median intraobserver agreement was substantial (Cohen's κ 0.738). CONCLUSIONS: The FOCUS classification provides clinically meaningful risk stratification for flat-type dysplasia in a high-risk UCAN cohort, with acceptable interobserver and intraobserver reproducibility.