Impact of Cutaneous Squamous Cell Carcinoma Histologic Features on Percent Interrater Agreement Regarding Tumor Differentiation

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.