A uniform residual tumor (R) classification: Integration of the R classification and the circumferential margin status

BACKGROUND: Since the introduction of the TNM residual tumor (R) classification, the involvement of resection margins has been defined either as a microscopic (R1) or a macroscopic (R2) demonstration of tumor directly at the resection margin ("tumor transected"). METHODS: The recognition of the importance of the circumferential resection margin (CRM) in patients with rectal cancer patients raises the need for an alternative definition of resection margin involvement, namely, the importance of delineating tumor with a minimal distance from the CRM of ≤1 mm (CRM-positive) from tumor directly at the resection margin. The different use of both definitions of resection margin involvement prevents valid comparisons between reports on treatment results. RESULTS: To avoid confusion by different definitions, the authors proposed including the minimal distance between tumor and resection margin into the current R classification. CONCLUSIONS: By using the proposed expanded classification, comparisons of new data with previous publications will be possible.