Background: Poor differentiation predicts adverse outcomes in cutaneous squamous cell carcinoma (CSCC), but there is no standardized, reliable grading system.
Objective: To explore which histologic features have the greatest impact on CSCC differentiation interrater agreement.
Materials and methods: In a prior study, 40 raters graded differentiation for 45 squamous cell carcinomas, and percent interrater agreements were calculated. Cases graded as well/moderately differentiated with 100% agreement (10), those graded as poorly differentiated with ≥80% agreement (5), and those that received a variety of grades with ≤60% agreement (7) were pulled for the current study. Three raters graded individual histologic features for each case, and percent interrater agreements were calculated using both the well/moderately/poorly differentiated grading system and a dichotomized system.
Results: The percent interrater agreements were 34.8% for mitoses, 53% for pleomorphism, 59.1% for keratinization, 66.7% for cellular cohesion/intercellular bridges, and 78.8% for tumor edges. Percent agreements improved with dichotomous grading; the largest improvement was seen within the group of cases that had been graded as well/moderately differentiated with 100% agreement in the prior study.
Conclusion: Future squamous cell carcinoma differentiation grading systems would benefit from eliminating mitotic rate, clearly defining how to grade other features, and dichotomous grading.
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