Long-term imaging characteristics of clinical complete responders during watch-and-wait for rectal cancer—an evaluation of over 1500 MRIs
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Rectal cancer patients with a clinical complete response after chemoradiotherapy (CRT) may be followed with a ‘watch-and-wait’ (W&W) approach as an alternative to surgery. MRI plays an important role in the follow-up of these patients, but basic knowledge on what to expect from the morphology of the irradiated tumour bed during follow-up is lacking, which can hamper image interpretation. The objective was to establish the spectrum of non-suspicious findings during long-term (> 2 years) follow-up in patients with a sustained clinical complete response undergoing W&W.
A total of 1509 T2W MRIs of 164 sustained complete responders undergoing W&W were retrospectively evaluated. Morphology of the tumour bed was evaluated (2 independent readers) on the restaging MRI and on the various follow-up MRIs and classified as (a) no fibrosis, (b) minimal fibrosis, (c) full thickness fibrosis, or (d) irregular fibrosis. Any changes occurring during follow-up were documented.
A total of 104 patients (63%) showed minimal fibrosis, 38 (23%) full thickness fibrosis, 8 (5%) irregular fibrosis, and 14 (9%) no fibrosis. In 93% of patients, the morphology remained completely stable during follow-up; in 7%, a minor increase/decrease in fibrosis was observed. Interobserver agreement was excellent (κ 0.90).
Typically, the morphology as established at restaging remains completely unchanged. The majority of patients show fibrosis with the predominant pattern being a minimal fibrosis confined to the rectal wall. Complete absence of fibrosis occurs in only 1/10 cases. Once validated in independent cohorts, these findings may serve as a reference for radiologists involved in the clinical follow-up of W&W patients.
• In rectal cancer patients with a sustained complete response after chemoradiation, the rectal wall morphology as established on restaging MRI typically remains unchanged during long-term MRI follow-up.
• The vast majority of complete responders show fibrosis with the predominant pattern being a minimal fibrotic remnant that remains confined to the rectal wall; complete absence of fibrosis occurs in only 10% of the cases.
• Once validated in independent cohorts, the findings of this study may serve as a reference for radiologists involved in the clinical follow-up of rectal cancer patients undergoing watch-and-wait.
KeywordsRectal neoplasms Magnetic resonance imaging Fibrosis
European Society of Gastrointestinal and Abdominal Radiology
Fast spin echo
The authors state that this work has not received any funding.
Compliance with ethical standards
The scientific guarantor of this publication is Doenja Lambregts.
Conflict of interest
The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.
Statistics and biometry
No complex statistical methods were necessary for this paper.
Written informed consent was waived by the Institutional Review Board.
Institutional Review Board approval was obtained.
Study subjects or cohorts overlap
The study patients were all selected from consecutive cohorts of previously reported and ongoing clinical trials focussing on the oncological and functional outcome of a watch-and-wait policy (Maas et al JCO 2011, Martens et al J Natl Cancer Inst 2016, van der Valk et al Lancet 2018, and an ongoing clinical study registered at clinical trials.gov under NCT03426397). In addition, 47 of the patients included in the current study were included in a previous study on the use of MRI+DWI to detect local tumour regrowths during follow-up (Lambregts et al Eur Rad 2016). This previous study concerned a diagnostic accuracy study focussing on detecting recurrent tumours with a specific focus on DWI, while the current report is a descriptive study focussing on T2W morphology which included only non-recurrent patients.
• Diagnostic or prognostic study
• Multicentre study
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