MRI for Selection of Complete Responders After Chemoradiation for Locally Advanced Rectal Cancer

Overview

The purpose of our study is to evaluate the accuracy of MRI for selection of complete responders after chemoradiation for locally advanced rectal cancer .

The current standard of care for patients with T3 or T4 and/or node-positive rectal adenocarcinoma is to offer preoperative concomitant chemoradiotherapy(CRT) followed by total mesorectal excision (TME). 1 In 10-24% of patients, no residual tumor is found at histology after surgery.2 These complete responders are known to have a very good prognosis, in terms of overall and disease-free survival.2 A complete response also raises the hotly debated question of whether surgery is still necessary for these patients, especially because total mesorectal excision (TME) may have associated morbidity and even mortality and has the potential risk of a permanent colostomy. Recently, a more conservative treatment is advocated in patients who show a good or complete response to neoadjuvant treatment. In 2006, Habr-Gama et al. Presented the long-term results of a prospective trial that investigated a "wait-and-see" policy in a carefully selected group of patients with clinical and radiological evidence of a complete response after neoadjuvant CRT. Results at 5-year follow-up were favorable for the nonsurgical group, with an overall and disease-free survival of 93% and 85%, respectively 3. Recently, A watch and wait policy avoids the morbidity associated with radical surgery and preserves oncologic outcomes. It could be considered a therapeutic option in patients with locally advanced rectal cancer following chemoradiotherapy with a complete clinical response.4 To safely omit surgery, it is essential to select accurately the right candidates, i.e., the true complete responders. This selection is mainly performed using digital examination, endoscopy, and biopsy, but these methods are not infallible. High-resolution magnetic resonance imaging (MRI) has been used to assess tumor response before surgical resection. By applying the principals of histopathologic TRG and by exploiting the characteristic MRI low-signal-intensity appearances of fibrosis, it has been possible to develop a similar MRI-based TRG system. The MRI-assessed TRG (mrTRG) was found to be an independent prognostic factor for overall survival (OS) and DFS.5 Complete pathologic response (pCR) after CRT has led to the proposal of a nonoperative approach as an alternate treatment for highly selected patients with a complete clinical response (CR). Habr-Gama et al reported findings from 99 patients with a clinical CR who were treated with observation alone. The 5-year OS and DFS rates were 93% and 85%, respectively.6 In a recent study, MRI-assessed complete tumor response was strongly correlated with pathologic complete response and, therefore, can be used as a surrogate marker to predict absence of viable tumor cells.7 Recently, Diffusion-weighted MRI (DWI) could be useful for response evaluation after chemoradiation treatment (8-10) In 2009, Kim et al. showed in a study of 40 patients that DWI in addition to standard MRI significantly improved the performance of radiologists to select complete responders compared with standard MRI only

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