Adopted in 1987 by the UICC.
Pertains to absence or presence of residual tumor after surgical treatment.
Residual tumor may be localized in the area of the primary tumor and/or as distant metastases.
R0 corresponds to resection for cure or complete remission.
R1 refers to microscopic residual tumor, and R2 to macroscopic residual tumor.
R classification takes into account clinical and pathological findings and requires the pathological examination of resection margins.
The R classification is a strong predictor of prognosis.