Evaluation of tumour response after radiotherapy in rectal cancer

The current interest in organ preservation and the watch-and-wait approach has renewed the interest to assess the response after (chemo)radiation, with the goal to identify patients with a complete or very good response. The most accurate identification is achieved with a combination of digital rectal examination, endoscopy and MRI. At present there is little evidence for a role for EUS and PET, and the role of a biopsy is unclear. The detection of small islands of tumour cells in the radiotherapy-induced fibrosis remains difficult with any technique. When the goal is to increase the number of patients who can avoid a major rectal resection, patients with a very good response can be selected for a prolonged observation period with a second assessment 8-12 weeks later. This allows for a better healing of the bowel wall, and a better identification of a complete response. A key element in this approach is to involve the patient in the decision-making process.