Preoperative MRI assessment of rectal cancer for predicting metastasis-free survival-a post hoc analysis of a randomized controlled clinical trial.

Abstract

This study aimed to evaluate preoperative MRI risk factors for metastatic disease in patients who underwent neoadjuvant chemoradiotherapy (nCRT) and curative surgery, followed or not by adjuvant chemotherapy (ChT). Single-center post hoc analysis of a randomized clinical trial data to evaluate the effect of adjuvant ChT in comparison to observation in patients with rectal cancer receiving nCRT and surgical resection. Preoperative MRI variables were retrospectively reviewed by three observers. Clinical, surgical, and pathological variables were included in univariate and multivariate analysis, and metastasis risk was assessed. A subgroup analysis was further performed to evaluate the effect of ChT on metastasis incidence in both good and poor responders to neoadjuvant treatment. A total of 132 patients (54% female, median age 55 years) were included. Poor mrTRG (HR = 2.53, 95% CI 1.32-5.65) and stage pIII disease (HR 1.94, 95% CI 1.09-3.45) were associated with increased metastatic risk. Although the rate of metastasis was lower in the treated group (9.1%) than in the control group (26.1%) among the patients who achieved a good response (mrTRG 1-2), the difference was not statistically significant (p = 0.19). The subgroup analysis revealed no difference in metastasis rates between patients with poor response receiving or not receiving adjuvant ChT. Response assessed by mrTRG is a preoperative prognostic factor associated with increased metastasis-free survival. MRI restaging could not predict the clinical benefits of adjuvant oxaliplatin-based ChT. Question To patients who have rectal cancer, the prediction of risk for metastatic disease during baseline staging to indicate systemic chemotherapy remains challenging. Findings MR-assessed poor tumor regression grade after neoadjuvant chemoradiotherapy (mrTRG3-5) and pathological postoperative nodal positivity are associated with increased metastatic risk. Clinical relevance The unpredictable response to neoadjuvant chemoradiotherapy is a significant driver of prognosis. The metastasis rates among good and poor responders receiving or not receiving adjuvant chemotherapy were similar. Challenges remain in selecting the population that will benefit from additional treatment.