Results
The search yielded a total of 122 specimens from 104 patients after appropriate exclusions. We examined a total of 122 BCC biopsy specimens with negative initial margins: 121 (99.2%) shave biopsies and 1 (0.8%) punch biopsy. Of 122 specimens with negative initial margins, 53 (43.4%) were found to have a truly positive margin based on the presence of either tumor or stroma at the lateral or deep tissue edge after complete tissue block sectioning. Sixty-nine (56.6%) specimens had clear margins and were categorized as truly negative after complete tissue block sectioning. Specimens with positive and negative final margin status did not differ significantly with respect to patient age; gender; biopsy technique; number of gross specimen sections; or tumor characteristics, including location, size, and subtype (Table)(P>.05).
We also examined the type of treatment performed, which varied and included curettage, electrodesiccation and curettage, excision, and Mohs micrographic surgery. Clinicians, who were not made aware of the exhaust level protocol, chose not to pursue further treatment in 6 (4.9%) of the cases because of negative biopsy margins. Four (66.7%) of the 6 providers were physicians, and 2 (33.3%) were advanced practitioners. All of the providers practiced within the Department of Dermatology.
Comment
Our findings support prior smaller studies investigating this topic. A prospective study by Schnebelen et al4 examined 27 BCC biopsy specimens and found that 8 (30%) were erroneously classified as negative on routine examination. This study similarly determined true margin status by assessing the margins at complete tissue block exhaustion.4 Willardson et al5 also demonstrated the poor predictive value of margin status based on the presence of residual BCC in subsequent excisions. They found that 34 (24%) of 143 cases with negative biopsy margins contained residual tumor in the corresponding excision.5
Our study revealed that almost half of BCC biopsy specimens that had negative histologic margins with routine sectioning had truly positive margins on complete block exhaustion. This finding was independent of multiple factors, including tumor subtype, indicating that even nonaggressive tumors are prone to false-negative margin reports. We also found that reports of negative margins persuaded some clinicians to forgo definitive treatment. This study serves to remind clinicians of the limitations of margin assessment and provides impetus for dermatopathologists to consider modifying how margin status is reported.
Limitations of this study include a small number of cases and limited generalizability. Institutions that routinely examine more levels of each biopsy specimen may be less likely to erroneously categorize a positive margin as negative. Furthermore, despite exhausting the tissue block, we still may have underestimated the number of cases with truly positive margins, as this method inherently does not allow for complete margin examination.
Acknowledgments
We thank the Geisinger Department of Dermatopathology and the Geisinger Biostatistics & Research Data Core (Danville, Pennsylvania) for their assistance with our project.