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. This study aimed to quantify the degree of shrinkage after fixation in formalin and to investigate the factors affecting specimen shrinkage. Methods: This research was a single-center 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 tumor. 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 tumor size. Conclusions: Specimens resected during anterior resection for colorectal cancer have a consistent level of shrinkage. Locally advanced tumors 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.