Alteration of Apparent Diffusion Coefficient Measurements Predict Survival Outcomes During Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer.

Background/aim: 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, this study aimed to identify apparent diffusion coefficient (ADC) values that predict survival outcomes after nCRT in patients with LARC.

Patients and methods: We analyzed data from 66 patients with LARC who underwent nCRT and evaluated the ADC values pre- and post-nCRT. Cox proportional hazard regression analyses were conducted to assess survival outcomes.

Results: There were no significant differences in disease-free survival (DFS) and overall survival (OS) between low and high ADC values 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, p<0.01; multivariate: p=0.01]. Finally, we identified ADC values that were significantly superior in predicting tumor regression grade, demonstrating remarkable diagnostic accuracy [post-nCRT: area under the curve (AUC)=0.79; alteration-nCRT: AUC=0.85].

Conclusion: We identified the clinical importance of changes in ADC values as a predictor of survival outcomes in patients with LARC. These results highlight the clinical importance of ADC values on improving the treatment strategies of patients.