- The T corresponds to the larger dimension of tumor at the rectal examination and the N is assessed by imaging pelvic MRI-imaging, CT-scan, optionally PET-CT). Eligible tumors are: T2 more than 4 cm N0-N3, T2-T4 N1-N3 or usN1, T3-T4 N0, M0 according to the 6th edition of the American Joint Committee on cancer staging manual.