Watch-and-wait strategy in rectal cancer is gaining momentum. There is a large variability in reporting the proportion of patients achieving clinical complete response (cCR) after routinely delivered preoperative radio(chemo)therapy, likely because of patients' selection. This proportion in population-based level is poorly defined. In addition, predictive factors for cCR are also poorly defined. It is known that cCR response is observed often in small tumours. However, cCR proportion in large cancers has not been sufficiently evaluated. For example, even though pathological complete response (pCR) does occur in large fixed cancer, it is unknown whether cCR does also occur because persistent fibrous stroma may mimic residual cancer in all of such cases.

This is a prospective observational population-based cohort study on low rectal cancer to answer the question of how often clinical or near-clinical tumour response occur after routinely delivered preoperative radiotherapy in relation to the pre-treatment tumour characteristics. The additional question was how often pCR occur in relation to the pre-treatment tumour characteristics in the patients managed by total mesorectal excision because of persistent tumour after radiotherapy. The additional aim was the implementation of watch-and-wait strategy or full-thickness local excision (as an option instead of total mesorectal excision in the patients with sustained near-cCR) within a frame of a prospective study. In the patients managed by organ preservation, the secondary outcome measures were: i) local regrowth rate, ii) effectiveness of salvage surgery, iii) disease-free survival at 3 years and overall survival at 5 years, iv) anorectal function.

Inclusion Criteria:

• Primary rectal cancer
• Low tumour (accessible by digital rectal examination)
• Routine preoperative radio(chemo)therapy according to the institutional policy; short-course radiation and immediate surgery is not allowed.
• Informed consent for watch-and-wait strategy or local excision in patients with cCR and near-cCR

Exclusion Criteria:

• Recurrent cancer
• Cancers situated in the upper rectum
• Distant metastases

140 patients with "resectable" cancer and 75 patients with threatened mesorectal fascia as assessed on multidisciplinary tumor board.