The neoadjuvant rectal score and a novel magnetic resonance imaging based neoadjuvant rectal score are stage independent predictors of long‐term outcome in locally advanced rectal cancer

Abstract

AbstractAimNeoadjuvant rectal (NAR) score is an early surrogate for longer‐term outcomes in rectal cancer undergoing radiotherapy and resection. In an era of increasing organ preservation, resection specimens are not always available to calculate the NAR score. Post‐treatment magnetic resonance imaging (MRI) re‐staging of regression is subjective, limiting reproducibility. We explored the potential for a novel MRI‐based NAR score (mrNAR) adapted from the NAR formula.MethodsLocally advanced rectal cancer patients undergoing neoadjuvant therapy (nCRT) and surgery were retrospectively identified between 2008 and 2020 in a single cancer network. mrNAR was calculated by adapting the NAR formula, replacing pathological (p) stages with post‐nCRT MR stages (ymr). Cox regression assessed relationships between clinicopathological characteristics, NAR and mrNAR with overall survival (OS) and recurrence‐free survival (RFS).ResultsIn total, 381 NAR and 177 mrNAR scores were calculated. On univariate analysis NAR related to OS (hazard ratio [HR] 2.05, 95% confidence interval [CI] 1.33–3.14, p = 0.001) and RFS (HR 2.52, 95% CI 1.77–3.59, p = 0.001). NAR 3‐year OS <8 was 95.3%, 8–16 was 88.6% and >16 was 80%. mrNAR related to OS (HR 2.96, 95% CI 1.38–6.34, p = 0.005) and RFS (HR 2.99, 95% CI 1.49–6.00, p = 0.002). 3‐year OS for mrNAR <8 was 96.2%, 8–16 was 92.4% and >16 was 78%. On multivariate analysis, mrNAR was a stage‐independent predictor of OS and RFS. mrNAR corresponded to NAR score category in only 15% (positive predictive value 0.23) and 47.5% (positive predictive value 0.48) of cases for categories <8 and >16, respectively.ConclusionsNeoadjuvant rectal score is validated as a surrogate end‐point for long‐term outcomes. mrNAR categories do not correlate with NAR but have stage‐independent prognostic value. mrNAR may represent a novel surrogate end‐point for future neoadjuvant treatments that focus on organ preservation.