Residual tumor classification

Last revised by Daniel J Bell on 8 Dec 2022

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.


  • 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.

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