There has been no published study estimating the proportion of positive surgical margins that is missed when serial transverse cross-sectioning (bread-loafing) is used to histologically evaluate the surgical margins.

Our purpose was to estimate the accuracy of serial transverse cross-sectioning (bread-loafing) at 4-mm intervals in detecting the presence of residual tumor at the margins of well-defined facial basal cell carcinomas excised as an ellipse with 2-mm surgical margins.

Forty-two small (<1 cm), well-defined, primary, nonmorpheaform facial basal cell carcinomas that had been excised as an ellipse with 2-mm margins and that had positive surgical margins utilizing en-face Mohs sections were included. After longitudinal bisection of each ellipse, frozen sections were prepared encompassing the entire surgical margin. Transparencies with parallel lines spaced at 4-mm intervals were superimposed on the histologic slides with the lines perpendicular to the epidermal surface. Areas in which the lines intersected tumor at the surgical margin were noted. The percentage of tumors that would be detected by serial cross sections was calculated on the basis of the percentage of these parallel lines that intersected tumor.

The 42 tumors had a total of 50 positive surgical margins. Overall, the cross-sectional lines intersected tumor 44% of the time (95% confidence interval, 37%-51%). Only 5 (10%) of the residual tumors at the surgical margins exceeded 4 mm in their longitudinal dimension. In the 9 sections containing tumor in the deep margin, tumor intersected the lines 39% of the time.

Bread-loafing at 4-mm intervals of elliptical excision specimens from facial basal cell carcinomas excised with 2-mm surgical margins is only 44% sensitive in detecting residual tumor at the surgical margins. We recommend complete histologic margin control by using en face tissue orientation (Mohs technique) to identify residual tumor and reduce the risk of tumor recurrence after elliptical excision of facial basal cell carcinomas.