The heterogenous nature of in vivo basal cell carcinoma

BACKGROUND. There have been nearly 70 different histologic subtypes of basal cell carcinoma (BCC) described. Some of the subtypes have been shown to have clinical relevance. The degree to which one type may merge to another, within the same tumor mass, has been poorly studied. OBJECTIVE. To determine if BCCs maintain biopsy histology throughout the entire architecture of the tumor. METHOD. Tumors were evaluated with a prospective histologic analysis of all primary BCCs using the Mobs 'removal in layers' technique. All BCCs that required more than a single Mohs stage to clear were included in analysis. RESULTS. One hundred forty-nine tumors were examined. Fourteen of these were of mixed histologic subtype on biopsy and were not included in the analysis. Six biopsy specimens were inadequate to make a subtype diagnosis and were excluded from calculation. Of the remaining 129 tumors 59% maintained their biopsy diagnosis at first Mohs stage, and 49% at the second Mohs stage. Infiltrative tumors were the most likely to maintain their histologic subtype classification. Of the tumors that showed nodular BCC on biopsy, 13% were infiltrative or micronodular at first Mohs stage. CONCLUSION. While many BCCs demonstrate a single histological subtype, roughly 40% change in their microscopic appearance at the subclinical extension. This finding has the potential to alter therapy.