The primary objective is to describe the functional outcome of patients that choose for organ saving treatment.

Rectal cancer is a common form of cancer. Standard treatment for locally advanced rectal cancer is a long course of neoadjuvant radiation combined with chemotherapy (CRT) followed by resection. However, neoadjuvant CRT induces downsizing and downstaging, resulting in a complete response in 15-20% of the patients. In these patients surgery may be omitted. In the investigators previous study the investigators obtained good results with an organ saving treatment. Although the mortality and morbidity associated with radical surgery is avoided, the irradiated rectum remains in situ, possibly causing functional problems.

The primary objective is to describe the functional outcome of patients that choose for organ saving treatment. Functional outcome will be evaluated with questionnaires (quality of life) and manometric measurements (maximal resting pressure, maximal squeezing pressure, sphincter length, percentage asymmetry of the resting sphincter, sustained duration, length of the high pressure zone, rectoanal inhibitory reflex, rectal sensory threshold, and rectal compliance).

Secondary objectives include: the estimation of the cumulative risk of local failure within 5 years, the estimation of the cumulative risk of disease-free, distant-metastasis-free and overall survival within 5 years, determine the percentage of patients that chooses organ saving treatment instead of standard resection, determine the compliance to intensive follow-up, and compare the cost-effectiveness of organ saving treatment to standard surgical resection over a period of 5 years. These objectives will be assessed by frequent revision of the electronic patient file, as the patient is followed up to four times per year.

Study design: prospective observational registration study with 'invasive diagnostic procedures' Study population: The population will consist of patients, aged 18 years or older, with locally advanced rectal cancer who after chemoradiation have a clinical complete response (ycT0N0) or very good response (ycT1-2N0).

Main study parameters/endpoints: The main study endpoint is the functional outcome scores based on questionnaires and manometric measurements Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The questionnaires take approximately 20 minutes to complete. There is a relatively low rate of side effects associated with manometric measurements. Results of this study will contribute to better understanding of functional complaints after rectal cancer treatment.

Inclusion Criteria:

• 18 years old

• Patients with primary rectal cancer without distant metastases who underwent CRT and show clinical complete response or very good response :

  • Clinical complete response (ycT0N0) after neo-adjuvant chemoradiation will be determined clinically (digital rectal examination, endoscopy) and radiologically (contrast-enhanced-MRI)
  • Very good response (ycT1-2N0) after neo-adjuvant chemoradiation will be determined clinically (digital rectal examination, endoscopy) and radiologically (contrast-enhanced-MRI). These patients will undergo a TEM to resect the small residual tumor

• Comprehension of the alternative strategies and the concept of unknown risks are clear to the patient

• Choosing for the organ-saving treatment option (wait&see policy or TEM)

• Informed consent

Exclusion Criteria:

• Unable to understand or read Dutch
• Unwilling to comply to the questionnaires or manometric measurement.

The population will consist of patients, aged 18 years or older, with locally advanced rectal cancer who after chemoradiation have a clinical complete response (ycT0N0) or very good response (ycT1-2N0). Patients will be recruited from the outpatient clinic, by researchers or research nurses at Maastricht University Medical Center.