Concordance of Squamous Cell Carcinoma Histologic Grading Among Dermatopathologists and Mohs Surgeons

Background: Current staging systems for cutaneous squamous cell carcinoma (cSCC) incorporate histologic grade. There are no universally agreed on criteria to define differentiation for cSCC.

Objective: To determine the interrater and intrarater reliability among dermatopathologists and Mohs surgeons in grading histological differentiation for cSCC.

Methods and materials: One hundred thirty-one archived slides were selected. Three dermatopathologists and 3 Mohs surgeons graded the tumors in a blinded manner (Round 1). In an attempt to improve concordance, all 6 participants were then asked to regrade the tumors based on a devised quantitative grading scale (Round 2).

Results: For Round 1, overall κ was 0.56 corresponding to a weak agreement. κ for well, moderate, and poorly differentiated tumors was 0.68, 0.39, and 0.59, respectively, corresponding to moderate, minimal, and weak concordance. For Round 2 of the study, overall κ was 0.60, with κ = 0.75, 0.46, and 0.61 for well, moderate, and poorly differentiated tumors, respectively. Overall intrarater reliability was 0.70 (κ = 0.70, 0.77, 0.68, 0.71, 0.56, and 0.75), corresponding to a moderate concordance.

Conclusion: Overall concordance for cSCC histologic grading is weak to moderate among the experimental group. Substantial differences in concordance exist among histological degrees of differentiation, with lowest agreement in moderately differentiated tumors.