Distal Margin Shrinkage Factor – A Consideration Before Dividing the Specimen in Colorectal Cancer Surgery

Background - The risk of local recurrence in colorectal cancer has been associated with the length of clear distal margin in the specimen taken during original resection. It has been reported that there is significant specimen shrinkage after fixation in formalin. This study is aimed to quantify this degree of shrinkage and to investigate the factors for specimen shrinkage. Methods – This research was a single centre prospective study. All adult patients who underwent colorectal surgery for cancer had demographics, surgical details and cancer staging and pathology recorded. Colonic specimens were measured immediately post resection including the total length, the mesenteric length and the distal length from the palpable tumour. Multiple logistic linear regression was applied to identify factors associated with distal margin shrinkage. Results – Right-sided colectomy specimens had an inconsistent degree of shrinkage. Left-sided colectomy specimens showed an average shrinkage of 20% (CI 4% – 36%). The only other factor observed that had statistically significant association on the shrinkage of distal margins in specimens was increasing tumour size. Conclusions - Specimens resected during anterior resection for colorectal cancer have a consistent level of shrinkage. Locally advanced tumours were observed to have an association with specimen distal margin shrinkage, however the mechanism is unclear. This new evidence can assist intra-operative decision making to allow adequate distal margin resection.