Neoadjuvant Chemotherapy, Excision And Observation vs Chemoradiotherapy For Rectal Cancer

Inclusion Criteria: * Histologically confirmed invasive, well-moderately differentiated rectal adenocarcinoma, mismatch repair proficient. * MRI stage cT1 not eligible for transanal surgery or cT2-T3ab\*. \* T3a: \<1mm depth invasion, T3b: 1-5mm depth of invasion. * cN0 stage based on pelvic MRI - including absence of radiographic evidence of mesorectal nodal metastasis, tumour deposits or extramural venous invasion (EMVI). * M0 stage based on no evidence of metastatic disease by CT imaging of chest, abdomen and pelvis. * Mid to low-lying tumour eligible for transanal excision in the opinion of the treating surgeon. * Medically fit to undergo radical TME surgery as per treating surgeon's decision. * Participant is able (i.e. sufficiently fluent) and willing to complete the quality of life questionnaires in either English or French or Spanish. * Age of at least 18 years. * No contraindications to protocol chemotherapy. * Adequate normal organ and marrow function: ANC ≥ x 10\^9/L; platelet count ≥ 100 x 10\^9/L; bilirubin \< 1.5 UNL, excluding Gilbert's syndrome; Estimated creatinine clearance of ≥ 50ml/min * Patient must have an ECOG performance of \<2 (or Karnofsty ≥ 60%). * Must be accessible for treatment and follow-up * Males and females of reproductive potential must have agreed to use a highly effective contraceptive method during and for 6 months after completion of chemotherapy. * HIV-infected patients on effective anti-retroviral therapy with undetectable viral load …