Re-staging and follow-up of rectal cancer patients with MR imaging when Watch-and-Wait is an option: a practical guide

In the past nearly 20 years, organ-sparing when no apparent viable tumour is present after neoadjuvant therapy has taken an increasingly relevant role in the therapeutic management of locally-advanced rectal cancer patients. The decision to include a patient or not in a Watch-and-Wait program relies mainly on endoscopic assessment by skilled surgeons, and MR imaging by experienced radiologists. Strict surveillance using the same modalities is required, given the chance of a local regrowth is of approximately 25-30%, almost always surgically salvageable if caught early. Local regrowths occur at the endoluminal aspect of the primary tumour bed in almost 90% of patients, but the rest are deep within it or outside the rectal wall, in which case detection relies solely on MR Imaging. In this educational review, we provide a practical guide for radiologists who are, or intend to be, involved in the re-staging and follow-up of rectal cancer patients in institutions with an established Watch-and-Wait program. First, we discuss patient preparation and MR imaging acquisition technique. Second, we focus on the re-staging MR imaging examination and review the imaging findings that allow us to assess response. Third, we focus on follow-up assessments of patients who defer surgery and confer about the early signs that may indicate a sustained/non-sustained complete response, a rectal/extra-rectal regrowth, and the particular prognosis of the near-complete responders. Finally, we discuss our proposed report template.

Automated summary

Organ-sparing therapy has become increasingly relevant in the management of locally-advanced rectal cancer patients who show no apparent viable tumor after neoadjuvant therapy. Assessment for inclusion in a Watch-and-Wait program relies on endoscopic evaluation and MR imaging, with a chance of local regrowth being approximately 25-30%, mostly surgically salvageable if detected early. Strict surveillance is necessary for early detection and management.