Abstract

Diagnosis of basal cell carcinoma (BCC) high risk subtypes influences management strategies because of their propensity to recur locally. Subtyping is prone to inter-observer variability, and subtyping definitions are not well understood. This study sought to compare the interobserver reproducibility of BCC subtypes using the 4th edition WHO Classification of Skin Tumours (CoST) definitions, with subclassification into low and high risk subtypes. A representative hematoxylin and eosin slide from 91 randomly selected cases of BCC was retrieved, following a database search, with an effort to incorporate the variety of BCC subtypes described in the 4th WHO CoST. All slides were blindly rated by 7 pathologists with variable experience, noting the presence of BCC subtype(s), and providing a high or low risk subtype grouping per case. Raters were provided with definitions as per the 4th edition WHO CoST for 10 listed BCC subtypes (5 high risk, 5 low risk). Surgical specimen type was noted. Subgroup analysis was performed to exclude cases when the tumor deep front was not well-visualized, or there was tangential sectioning (n=6). Light’s kappa was used to assess inter-rater reliability. From the total group (n=91), 5 BCC subtypes showed a sufficient number of ratings for computing a κ statistic. Superficial subtype showed substantial inter-rater agreement (κ=0.64), and the other 4 subtypes showed moderate inter-rater agreement (nodular (κ=0.45), sclerosing/morphoeic (κ=0.45), infiltrating (κ=0.49) and micronodular (κ=0.57)). In the subgroup (n=85), no relevant difference between these cases and the total group was detected. Two-tiered rating into either high or low risk subtype showed substantial inter-rater agreement (κ=0.72). Our results suggest a need to more precisely define BCC subtypes. Unification of selected high and low risk subtypes would improve inter-rater reliability. We suggest reporting BCC subtype using a two-tiered risk grouping, followed by specific subtypes present.

Financial Disclosure:
No current or relevant financial relationships exist.