Predictive value of margins in diagnostic biopsies of nonmelanoma skin cancers

Background: With geographic regional variation, nonmelanoma skin cancer biopsy reports include assessment of margins. When margins are reported as negative, clinical dilemmas may emerge concerning the necessity of additional treatment. Objective: To evaluate the predictive value of biopsy margins with regard to residual tumor present in subsequent excisions of nonmelanoma skin cancers. Methods: This is a retrospective review of 235 diagnostic nonmelanoma skin cancer biopsies and their corresponding excisions for margin status at biopsy, and the presence of residual tumor in subsequent excisions. Results: Twelve of 148 squamous cell carcinomas (8.1%) had negative biopsy margins and all of the subsequent excisions were free of residual tumor. The squamous cell carcinomas with negative biopsy margins consisted predominantly of nonfacial, superficial tumors of the well-differentiated and keratoacanthoma subtype. Nine of 87 basal cell carcinomas (10.3%) had negative biopsy margins. Seven of those 9 (77.8%) had residual tumor present in subsequent excisions. Limitations: Statistical analysis performed reached significance, but with small sample size as only 21 of the biopsy specimens had negative margins. Also, residual tumor was determined via standard bread-loafing technique on excisions, which is known to examine only a proportion of the tissue and can lead to false-negative results. Conclusions: The results of this small pilot study suggest that negative-margin diagnostic biopsies may be therapeutic for well-differentiated or keratoacanthoma subtypes of squamous cell carcinoma because all subsequent excisions were devoid of tumor. Negative biopsy margins from basal cell carcinomas were not predictive of tumor removal.