Alteration of apparent diffusion coefficient measurements predict survival outcomes during neoadjuvant chemoradiotherapy in locally advanced rectal cancer

Abstract Background Neoadjuvant chemoradiation therapy (nCRT) followed by surgery is recommended for patients with locally advanced rectal cancer (LARC). However, because 30–40% of patients with LARC do not respond to nCRT, better prediction of treatment responses and survival outcomes is required. Therefore, we aimed to identify apparent diffusion coefficient (ADC) values that predict survival outcomes after nCRT in patients with LARC. Methods We analyzed 66 patients with LARC who underwent nCRT and evaluated ADC values of pre- and post-nCRT. We performed Cox proportional hazard regression analyses for survival outcomes. Results There were no significant differences in disease-free survival (DFS) and overall survival (OS) between low and high ADC values of pre-nCRT. However, patients classified as low ADC in post-nCRT had a significantly worse prognosis in OS and DFS (OS: P = 0.01; DFS: P < 0.01) than patients classified as high ADC. Moreover, an alteration in ADC values between pre- and post-nCRT was associated with poor OS (univariate: hazard ratio [HR] = 4.52, 95% confidence interval [CI] = 1.58–12.97, P < 0.01; multivariate: HR = 6.38, 95% CI = 1.48–27.56, P = 0.01). Finally, we identified ADC values that were significantly superior for predicting tumor regression grade with remarkable diagnostic accuracy (post-nCRT: area under the curve [AUC] = 0.79; alteration-nCRT: AUC = 0.85). Conclusions We identified the clinical importance of alteration of ADC values to predict the survival outcomes in patients with LARC. These results highlight the clinical importance of ADC values on improving the treatment strategies of patients.