The apparent diffusion coefficient is a useful biomarker in predicting treatment response in patients with locally advanced rectal cancer

BACKGROUND: Apparent diffusion coefficient (ADC) values achieve promising results in treatment response prediction in patients with several types of cancers. PURPOSE: To determine whether ADC values predict neoadjuvant chemoradiation treatment (nCRT) response in patients with locally advanced rectal cancer (LARC). MATERIAL AND METHODS: Forty-four patients with LARC who underwent magnetic resonance imaging scans before and after nCRT followed by delayed surgery were enrolled retrospectively. The sample was distributed as follows: responders (R), n = 8; and non-responders (Non-R), n = 36. Three markers of treatment response were considered: post-nCRT measures; ΔADC; and Δ%ADC. Statistical analysis included a Wilcoxon test, a Mann–Whitney U test, and a receiver operating characteristic (ROC) analysis in order to evaluate the diagnostic accuracy for each ADC value marker to differentiate between R and Non-R. RESULTS: Both minimum and mean ADC values were significantly higher after nCRT in the R group, while non-significant differences between basal and control ADC values were found in the non-R group. In addition, ΔADC and Δ%ADC exhibited increased values after nCRT in R when compared with non-R. ROC analysis revealed the following diagnostic performance parameters: post-nCRT: ADC(min) = 1.05 × 10(−3) mm(2)/s (sensitivity 61.1% and specificity 66.7%), ADC(mean) = 1.50 × 10(−3) mm(2)/s (sensitivity 72.2% and specificity 83.3%), ΔADC: ADC(min) = 0.35 (sensitivity 66.7% and specificity 83.3%), ADC(mean) = 0.50 (sensitivity 72% and specificity 83%); and Δ%ADC: ADC(min) = 44% (sensitivity 66.7% and specificity 83.3%) and ADC(mean) = 60% (sensitivity 83% and specificity 99%). CONCLUSION: Our findings suggest that post-treatment rectal tumor ADC values, as well changes between pre- and post-treatment values, may be biomarkers for predicting treatment response in patients with LARC who underwent nCRT.