MRI Assessment and Outcomes in Patients Receiving Neoadjuvant Chemotherapy Only for Primary Rectal Cancer: Long-term Results from the GEMCAD 0801 Trial

Background: 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.

Patients And Methods: 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.

Results: About 46 patients underwent neoadjuvant chemotherapy alone for high risk margin safe primary rectal cancer. The median follow-up was 41 months, 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).

Conclusions: 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.