Abstract
e14097 Background: MRI methods for rectal cancer response assessment post chemoradiotherapy include post treatment T staging(ymrT), tumor regression grading(mrTRG) and length change/modified RECIST measurement. The usefulness of MRI in evaluating response to neoadjuvant chemotherapy has not been investigated. We assessed the reproducibility and agreement of these three parameters with histopathological T and TRG stage(ypT, pTRG). Methods: 28 eligible patients were enrolled in a prospective phase II trial to evaluate safety and efficacy of neoadjuvant CAPOX-B in patients with MRI defined T3 rectal adenocarcinoma. Patients received 4 cycles of Cap 2000 mg/m2(d1-14),Ox 130 mg/m2(d1) and B 7.5 mg/kg(d1) every 3 weeks(last cycle without B). Seven radiologists assessed MRIs using the following categories: ymrT (T0-T4 using T3 substaging), mrTRG (1-5), and length change(Stable disease, Complete response,Partial response). Agreement was assessed by kappa (central reviewer data verses each local centre reviewer).Agreement between central reviewer MRI results and both pathology endpoints was also assessed. Results: 24 patients had evaluable pre and post chemotherapy imaging and pathology (4 did not have post treatment MRI). Thirteen patients had good response (ypT0-3a) and 11 had poor response (>ypT3a). Sixteen patients had good pTRG(2-4) and 8 had poor pTRG(0&1). ymrTRG showed a moderate level of reproducibility;K=0.45-0.58. ymrT showed a fair to moderate level of agreement;K=0.2-0.53. Length assessment also showed a fair level of agreement; K=0.21-0.38. ymrTRG showed 75% agreement with ypT(16/22); K=0.49(0.13-0.84) and 79% agreement with pTRG(19/24); K=0.55(0.22-0.88). ymrT showed a fair level of agreement with ypT;K=0.21, pTRG;K=0.2, length assessment showed slight agreement with ypT;K=0.1, pTRG;K=0.1. Conclusions: This is the first study to show MRI can evaluate response of rectal cancer following neoadjuvant chemotherapy. As mrTRG showed best agreement with pathology, we recommend mrTRG as the preferred method of post treatment assessment in this setting.
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