Effect of tissue shrinkage on histological tumour-free margin after excision of basal cell carcinoma

Background Histology reports of skin tumour excisions frequently describe a histological margin significantly less than the planned surgical excision margin. Objectives A novel method of marking visible tumour margin was devised. This allowed us to evaluate the accuracy of tumour detection and to compare tissue contraction of the clinically normal perilesional skin with that of tumour tissue following excision and fixation. Methods Forty-four well-defined basal cell carcinomas were excised from 42 patients. The visible tumour edge was marked by scoring with a blade around its circumference prior to excision. This allowed comparison of visible and true histological tumour margin. The excision margin was carefully measured from the scored line and the tumour excised. After tissue fixation and processing the histological dimensions of tumour and perilesional margin skin were compared with the pre-excision measurements. Results The tumour edge was accurately identified to within 1 mm in 67% of margins and was underestimated in only 4%. The whole specimen contracted by a mean of 14%. Skin containing tumour contracted by a mean of 11% but adjacent tumour-free skin in the same plane contracted by a mean of 19%. There was no significant effect of age and site on difference in percentage shrinkage between tumour and margin. Conclusions We underestimated tumour extent at only 4% of margins. Tissue shrinkage was the most important factor affecting eventual histological margin. Our novel technique allowed us to demonstrate that this shrinkage is not uniform across the specimen, but is disproportionately high in the tumour-free margin. This suggests that previous estimates of margin shrinkage, based on whole-specimen contraction measurements, may have been erroneously low.