The high proportion of complete and good responders with modern chemoradiation and the improvement in magnetic resonance (MR)-imaging techniques have stimulated a renewed interest to the question whether in patients with complete or good response the overall benefits of a 'wait-and-see policy' or transanal endoscopic microsurgery (TEM) combined with intensive follow-up may outweigh the benefits associated with conventional surgery (total mesorectal excision (TME)or abdominoperineal resection (APR)). On the one hand, less invasive strategies will expose subjects to more diagnostic procedures and possibly a slightly higher risk of local failure and the need for salvage surgery. On the other hand, mortality and morbidity associated with radical surgery (e.g. anastomotic leakage, relaparotomy, wound and pelvic infection, chronic wound healing disturbances, abscess, colostomy, faecal or urinary incontinence and sexual dysfunction) can be avoided. The investigators believe that wait-and-see policy for complete responders and TEM for good responders after chemoradiation is a feasible alternative to standard surgery, provided these patients are intensively followed.

The high proportion of complete and good responders with modern chemoradiation and the improvement in magnetic resonance (MR)-imaging techniques have stimulated a renewed interest to the question whether in patients with complete or good response the overall benefits of a 'wait-and-see policy' or transanal endoscopic microsurgery (TEM) combined with intensive follow-up may outweigh the benefits associated with conventional surgery (total mesorectal excision (TME) or abdominoperineal resection (APR)). On the one hand, less invasive strategies will expose subjects to more diagnostic procedures and possibly a slightly higher risk of local failure and the need for salvage surgery. On the other hand, mortality and morbidity associated with radical surgery (e.g. anastomotic leakage, relaparotomy, wound and pelvic infection, chronic wound healing disturbances, abscess, colostomy, faecal or urinary incontinence and sexual dysfunction) can be avoided. The investigators believe that wait-and-see policy for complete responders and TEM for good responders after chemoradiation is a feasible alternative to standard surgery, provided these patients are intensively followed.

Inclusion Criteria:

• 18 years or older
• Patients with primary rectal cancer without distant metastases who underwent CRT and show clinical complete response or very good response: Clinical complete response (ycT0N0) or very good response (ycT1-2N0) after pre-operative chemoradiation will be determined clinically (digital rectal examination, endoscopy), radiologically (contrast-enhanced-MRI) and pathologically (biopsy)
• Informed consent and capability of giving informed consent
• Comprehension of the alternative strategies and the concept of unknown risks are clear to the patient (in other words that the patient understands the experimental base of the study).

Exclusion Criteria:

• Recurrent rectal cancer.
• Distant metastasis.
• Unable or unwilling to comply to the intensive follow-up schedule.
• Contra-indications for MRI. If MRI is not possible because of contra-indications (e.g. pacemaker) we will exclude patients. MRI is crucial for response evaluation and follow-up and can not be omitted in patients that follow the alternative strategies ('wait-and-see policy' or TEM).

Pooling of data is expected in the future