MRI assessment and outcomes in patients receiving neoadjuvant chemotherapy only for primary rectal cancer: long-term results from the GEMCAD 0801 trial

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Primary chemotherapy has been tested as a possible approach for patients with high risk features but predicted clear mesorectal margins on preoperative MRI assessment. This study investigates the prognostic relevance of baseline and post-treatment MRI and pathology staging in rectal cancer patients undergoing primary chemotherapy. Forty-six patients with T3 tumour > =2 mm from the mesorectal fascia were prospectively treated with Neoadjuvant Capecitabine, Oxaliplatin and Bevacizumab prior to surgery between 2009 and 2011. The baseline and post-treatment MRI: T, Nodal and Extra-mural venous invasion (EMVI) status were recorded as well as post-treatment MRI Tumour regression grade (TRG) and modified-RECIST assessment of tumour length. The post-treatment pathology (yp) assessments of T3 substage, N, EMVI and TRG status were also recorded. Three-year disease-free survival (DFS) and cumulative incidence of recurrence were estimated by using the Kaplan-Meier product-limit method, and Cox proportional hazards models were used to determine associations between staging and response on MRI and pathology with survival outcomes. About 46 patients underwent neoadjuvant chemotherapy alone for high risk margin safe primary rectal cancer. The median follow-up was 41months, 5 patients died and 11 patients experienced relapse (2 local, 8 distant and 1 both). In total 23/46 patients were identified with MRI features of EMVI at baseline. mrEMVI positive status carried independent prognostic significance for DFS (P = 0.0097) with a hazard ratio of 31.33 (95% CI: 2.3-425.4). The histopathologic factor that was of independent prognostic importance was a final ypT downstage of ypT3a or less, hazard ratio: 14.0 (95% CI: 1.5-132.5). mrEMVI is an independent prognostic factor at baseline for poor outcomes in rectal cancer treated with neoadjuvant chemotherapy while ≤ypT3a is associated with an improvement in DFS. Future preoperative therapy evaluation in rectal cancer patients will need to stratify treatment according to baseline EMVI status as a crucial risk factor for recurrence in patients with predicted CRM clear rectal cancer.