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Background There are numerous subtypes of basal cell carcinoma (BCC). Defining the histopathologic subtype is an essential element in patient management, but there is little known data regarding interobserver precision in subtyping BCC. Methods We studied interobserver variance between six board-certified dermatopathologists who subtyped 100 BCCs in a blinded fashion. We used kappa statistic to calculate the concordance in suggested subtype by different dermatopathologists. Provided diagnoses were then re-categorized into low-risk and high-risk phenotypes, and kappa statistic for concordance on high-risk BCC was determined. Results The overall κ statistic was 0.301, indicating fair agreement among the six observers. Superficial and fibroepithelial BCC had the highest individual kappa statistics. When subtypes were re-classified into a two-tier system of high-risk and low-risk phenotypes, there was substantial interobserver agreement on high-risk BCC with a κ statistic of 0.699. Conclusion These results suggest only fair agreement among dermatopathologists on specific BCC subtypes, but substantial agreement on superficial, fibroepithelial and high-risk BCC growth patterns. A simplified classification system comprised of superficial, fibroepithelial, nodular and infiltrative subtypes would increase interobserver precision and facilitate clinical decision-making.

The distinction between actinic keratosis (AK) and squamous cell carcinoma in-situ (SCCIS) is a subject of discussion among dermatopathologists. A previous study determined that there was excellent interobserver agreement among dermatopathologists using the current two-tiered grading system. Presently, we assessed concordance among dermatopathologists using a three-tiered keratinocytic intraepithelial neoplasia (KIN) diagnostic system. At the 2006 meeting of the American Society of Dermatopathology (ASDP), registration personnel solicited 125 registrants by randomly inserting an invitation into 125 registration packets. Participants reviewed 15 glass slides representing a spectrum of keratinocytic atypia from AK to SCCIS. Participants were asked to choose 1 or 2 but not 3 grades of KIN that best reflected the changes on each slide. Thirty-two of the 125 solicited enrollees participated in the study. There were 16 volunteers for a total of 48 participants. The inter-observer agreement for all participants was 0.575 (moderate agreement). The overall inter-observer agreement for anatomic pathologist-dermatopathologists (AP-DP), dermatopathologist-dermatologists (DP-D) and anatomic pathologist-dermatologist-dermatopathologists (AP-DP-D) was 0.665, 0.609 and 0.670 (substantial agreement), respectively. There is high concordance among dermatopathologists using a three-tiered diagnostic system for KIN. The observed agreement suggests that dermatopathologists are reliably able to categorize the continuum of keratinocytic atypia in a manner that may have diagnostic relevance.

Diagnostic concordance of intraepithelial malignancy is generally only fair. Because the diagnosis of actinic keratosis (AK) and squamous cell carcinoma (SCC) is not uniform and because such terms are not consonant with the nomenclature of other human epithelial malignancies, nomenclature revisions have been attempted. One hundred dermatopathologists were solicited to review 15 tissue sections representing a spectrum of varying thickness epidermal malignancy and to choose either AK or SCC as the diagnosis. Among the 77 participating dermatopathologists, intraclass correlation was high for what was perceived as AK, SCC, and their differentiation. Development of a two-tiered diagnostic system that retains our present diagnostic capabilities, but better fits the pathobiology of superficial epidermal malignancy is suggested. Davis DA, Donahue JP, Bost JE, Horn TD. The diagnostic concordance of actinic keratosis and squamous cell carcinoma.