Suspicion of adverse events

Among patients treated for locally advanced rectal cancer with neo-adjuvant radio-chemotherapy, about 15% will have complete clinical response in terms of no visible tumor or ulcerations on the site of the primary tumor, or whitening of the rectal wall or telangiectasia. In this Norwegian national multicenter observational study, patients with complete clinical response (cCR) after neo-adjuvant treatment for rectal cancer as defined by national guidelines, will be invited to a Watch&Wait program with a specially designed follow-up in order to see if the tumor has disappeared permanently, or if there is regrowth of the tumor. Primary endpoint is the true regrowth rate in an unselected national cohort of patients.

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

All patients in Norway with rectal cancer treated with neo-adjuvant radio-chemotherapy according to Norwegian national guidelines, who have complete clinical response at 6-12 weeks after fulfilled treatment