"Watch and Wait" After Neo-adjuvant Chemoradiotherapy for Primary Locally Advanced Rectal Cancer.

Inclusion Criteria: * Histologically verified adenocarcinoma of the rectum within 15 cm from the anal verge measured by rigid proctoscopy * Patients who have completed neoadjuvant treatment according to national guidelines for rectal cancer, i.e., radiotherapy or chemo-radiotherapy (at least 40 Gy) or short-course radiotherapy combined with chemotherapy * Patients aged ≥18 years of age are eligible for inclusion. However, patients aged ≤40 years are recommended to undergo surgery on the theoretical base of a possibly more aggressive tumour disease in this age group, and will be asked to participate in the study by consenting to recording of data. Those patients who insist on W\&W approach after careful consideration and well-documented informed consent are eligible for entering the W\&W protocol. * Given informed consent * Stage I-III rectal cancer; however, patients with limited liver metastases who undergo primary liver surgery as part of a "liver first" treatment approach may be included Exclusion Criteria: * Patients without cCR * Patients unable to give informed consent * Patients with short course radiotherapy (5x5 Gy) without additional chemotherapy, or patients receiving less than 40 Gy in long course CRT * Patients with cCR but with increasing tumour growth on MRI after preoperative treatment * Patients with metastatic disease at the time of diagnosis with the exception of those who are eligible for "liver first" treatment approach as part of an intention to cure approach. * Patients previously diagnosed and treated for malignant disease in the pelvic region with radio- or chemoradiotherapy * Other circumstances that may interfere with successful participation in the W\&W protocol