91P Prognostic biomarker of clinical outcome in locally advanced rectal cancer in Chinese patients

Neoadjuvant chemoradiotherapy (NCRT) is one of the standard treatments for locally advanced rectal cancer (LARC), where pathological complete response (ypCR) has been traditionally used as a surrogate survival endpoint. A relatively new biomarker known as the Neoadjuvant Rectal (NAR) score has been consistently shown to correlate with survival in clinical studies. NAR score is a composite endpoint combining clinical and pathological staging information obtained before and after NCRT which warrants validation in local population. The main objective of this study is to investigate the factors that may influence the achievement of ypCR, such as age, sex, tumour stage and location, presence of threatened CRM and extramural vascular invasion (EMVI) as well as tumour down-staging. Other objectives are to validate the prognostic significance of NAR score and to investigate any factors that are associated with a lower score. The data of patients with LARC who received NCRT at the Prince of Wales Hospital between August 2006 to October 2018 were retrospectively analyzed. Chi-square or Fisher’s Exact Test was used to determine any correlation between categorical variables and logistic regression for continuous variables. Cox regression was used to determine any interactions between covariates and Kaplan-Meier method for survival analysis. Of the 193 patients who had optimal response to NCRT and surgery, the mean age was 62 and the male-to-female ratio was 2.94: 1. Tumour down-staging was the only independent prognostic factor which predicted ypCR (p<0.0001). NAR score was associated with overall survival (OS) (hazard ratio, HR=1.042, 95% confidence interval, CI: 1.021-1.064, p<0.0001), disease-free survival (DFS) (HR=1.042, 95% CI: 1.022-1.062, p<0.0001), locoregional recurrence-free survival (LRFS) (HR=1.070, 95% CI:1.039-1.102, p<0.0001) and distant recurrence-free survival (DRFS) (HR=1.034, 95%CI: 1.012-1.056, p=0.002). Patients who had ypCR to NCRT was associated with a lower NAR score (p<0.0001), but ypCR was not associated with survival. NAR score (but not ypCR) is an independent prognostic marker of survival and disease recurrence in a cohort of Chinese patients who underwent NCRT for LARC.