Significance of Magnetic Resonance Imaging–Assessed Tumor Response for Locally Advanced Rectal Cancer Treated With Preoperative Long-Course Chemoradiation

Abstract

PurposeTo study the predictive and prognostic value of magnetic resonance imaging (MRI)–assessed tumor response after long-course neoadjuvant therapy for locally advanced rectal cancer.MethodsThis study included 79 patients who had T3 or T4 and/or N+ rectal cancer treated with long-course neoadjuvant chemoradiation. MRI-assessed tumor regression grade (mrTRG) was assessed in 64 patients. MRIs were reviewed by the study radiologist. Surgical and pathologic reports for those who underwent surgery were reviewed. Disease-free survival (DFS) was estimated. Progression during therapy, local relapse, metastasis, and death resulting from the tumor were classified as events. Statistical significance was calculated.ResultsIn 11 patients, the tumor completely disappeared on MRI; that is, it had an mrTRG of 1. All but one patient, who chose deferred surgery, had a complete pathologic response (pCR), with a positive predictive value of nearly 100%. Of the 20 patients who had an mrTRG of 2 on MRI, six had a pCR. mrTRG 3, mrTRG 4, and mrTRG 5 were detected in 24, six, and three patients, respectively, of whom only one patient had a pCR. The 2-year DFS was 77%. The mrTRG was significant for DFS. The 2-year DFS was 88% for patients with a good response versus 66% for those with a poor response (P = .046).ConclusionMRI-assessed complete tumor response was strongly correlated with pCR and, therefore, can be used as a surrogate marker to predict absence of viable tumor cells. Our results can be used to implement use of mrTRGs in larger prospective correlative studies as a tool to select patients for whom deferred surgery may be appropriate. Also, those with a poor response may be offered further treatment options before definitive surgery.

Morphologic predictors of pathological complete response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer

“…MR tumor regression grade (mrTRG) has been reported to be an excellent method for differentiating good from poor response in patients with rectal cancer [ 41 – 42 ]. Further studies need to be carried out in order to improve the interobserver consistency.…”

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

“…There are multiple ordinal scales in the literature that represent variations or adaptations to it but in general, when T2-WI intermediate “tumour” signal predominates over hypointense fibrosis or clear hyperintense “acellular mucin” (mrTRG4-5, mrTRG5 hardly ever being observed in our experience), a poor response is assumed, and the 3-year disease free survival is 21% inferior compared to favourable mrTRG1-3s [ 23 ]. mrTRG3 may fall on the “good side” regarding long-term outcome [ 26 ] but the likelihood of a pCR or cCR when T2-intermediate clearly “tumoural” signal remains after neoadjuvant treatment is low, and it is therefore considered a sign of an incomplete response [ 27 ]. Significant restriction to diffusion on Diffusion-weighted Imaging (DWI) …”

Diagnostic performance of MRI and endoscopy for assessing complete response in rectal cancer after neoadjuvant chemoradiotherapy: a systematic review of the literature

“…Study characteristics and methodological details are shown in Tables 1 and 2 and Supplemental Tables 4-10 (Supplemental material available online). Combined, 19 studies investigated T2-mrTRG (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43), 39 studies investigated DW-MRI (25,32,37,, 13 studies investigated PW-MRI (80)(81)(82)(83)(84)(85)(86)(87)(88)(89)(90)(91)(92), and 15 studies investigated endoscopy with or without MRI (26,36,(93)(94)(95)(96)(97)(98)(99)(100)(101)(102)…”

“…The PPV and NPV of T2-mrTRG grade 1 for detecting ypCR were in the range of 0%-99% and 73%-98%, respectively. The majority of studies (n = 17) were conducted retrospectively (25,(27)(28)(29)(30)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43). Sample sizes were in the range of 41-439 patients.…”

“…Sample sizes were in the range of 41-439 patients. Ten studies failed to report the use of consecutive patient enrollment (25,26,29,31,32,(34)(35)(36)39,43). All studies used long-course nCRT.…”