Residual tumor classification, also known as R classification, defines how complete the resection of a malignancy has been at surgery. It has an important prognostic implication.
Classification
R0: no residual tumor
R1: microscopic residual tumor
R2: macroscopic residual tumor
An R0 resection means that the surgical margin is microscopically-negative for residual tumor. An R1 resection means that there is no residual macroscopic tumor but that microscopically margins still demonstrate the presence of tumor. R2 resection means that gross (macroscopically-visible) disease remains post-surgery 1,2.
History and etymology
Surgeons have been aware for a long time that patient outcome after surgical removal of malignancy is directly related to how complete the resection of the tumor has been. However, it was not until 1978 that the American Joint Committee on Cancer introduced the residual tumor or R classification as an adjunct to the TNM staging system 1.