Diagnostic accuracy of punch biopsy in subtyping basal cell carcinoma.

Background: Basal cell carcinoma (BCC) is the most common skin cancer in humans. The histological subtype reported by punch biopsy may influence the type of treatment. Few studies have investigated the accuracy of punch biopsy in diagnosing the true BCC subtype.

Objective: To determine the accuracy, sensitivity and specificity of punch biopsy in BCC subtype diagnosis.

Methods: In this retrospective study, 333 biopsy specimens and excisions were reviewed. Histological subtypes present in the initial biopsy were compared with tumour subtypes of the total excision.

Results: The concordance between the BCC subtype present in the biopsy specimen and in the subsequent excision specimen was 72.3%. The most common BCC patterns were nodular (158, 47.5%) and mixed subtype (90, 27%). Most mixed tumours contained one or more aggressive subtype (63/90, 70%). In 47/120 (39.1%) aggressive tumours (14.1% of the total), punch biopsy failed to correctly identify the aggressive component. The most commonly missed aggressive subtype was mixed aggressive including nodular/micronodular and nodular/infiltrative (30/47, 63.8%). In 45/213 (21.1%) non-aggressive BCCs (13.5% of total cases), punch biopsy incorrectly reported an aggressive subtype. The most commonly misidentified non-aggressive subtype was nodular (39/45, 86.6). The sensitivity and specificity of punch biopsy in diagnosing aggressive vs. non-aggressive BCC subtypes 60.8% (95% CI, 51.9-69.1) and 78.9% (95% CI, 72.8-83.8), respectively. The positive and negative predictive values were 61.9% and 78.1%, respectively.

Conclusion: Punch biopsy has serious pitfalls in differentiating aggressive and non-aggressive BCC subtypes. Dermatologists should consider the possibility of aggressive components within non-aggressive BCCs reported using punch biopsy.