High discordance between punch biopsy and excision in establishing basal cell carcinoma subtype: analysis of 500 cases

Basal cell carcinoma (BCC) is the most frequently occurring cancer in humans. Worldwide incidences rise about 10% each year, increasing the burden on dermatologists, general practitioners and pathologists as well as increasing costs for the health care system. Increasingly non-surgical treatment options are used in the treatment of BCC, without histological confirmation of BCC subtype, potentially resulting in under-treatment.We evaluated the diagnostic accuracy of a punch biopsy for the BCC histological subytpe in a primary BCC and the prevalence of biopsy-based under-diagnosis of aggressive subtypes. Accuracy of a punch biopsy was defined as concordance of the diagnosis of subtype of BCC at punch biopsy and excision.A retrospective chart-review was performed of primary BCC, which were proven by punch biopsy and subsequently treated by excision. The first 100 consecutive BCCs per year during the years 2004-2009 were included, yielding a total of 500 evaluated BCCs.The overall accuracy of punch biopsy for BCC subtype at excision was 69%, in single-type BCC 83% (n = 343) and in mixed-type BCC 37% (n = 157). Accuracy varied substantially according to BCC subtype, being highest in the superficial subtype (84%) and subsequently in infiltrative (69%), nodular (63%) and micronodular subtype (38%). In 11% of all cases, an unsuspected more aggressive subtype was present.Punch biopsy has a high accuracy in single-type BCCs and a considerably lower accuracy in mixed-type BCCs for establishing BCC subtype compared to excision. The presence of an unsuspected aggressive subtype could explain therapy failure of non-surgical treatments like imiquimod or photodynamic therapy.