Changes in apparent diffusion coefficient evaluated with diffusion-weighted MRI to predict complete pathologic response after neoadjuvant therapy for rectal cancer: Literature review and meta-analysis.

503 Background: A complete pathological response (pCR) is observed in 9-38% of all patients undergoing neo-adjuvant chemo-radiation therapy (CRT) for locally advanced rectal cancer (ARC). Imaging techniques that can reliably assess CRT results may enhance identification of those pCR patients for which surgery may potentially be avoided. Recently, several studies have suggested that diffusion-weighted magnetic resonance imaging (DW-MRI) may predict pathologic response by measuring tumor apparent diffusion coefficient (ADC). ADC can be measured before (pre-ADC) and/or after CRT (post-ADC). Both pre- and post-ADC, as well as the variation between pre- and post-ADC (Δ-ADC) can be used to assess pCR. We aimed to assess the reliability of ADC at predicting pCR in ARC patients treated with CRT. To determine the most effective ADC timing to evaluate pCR. Methods: A systematic review of available literature was conducted to compare all the studies of DW-MRI for identification of pCR after CRT for ARC. For each parameter (pre-ADC, post-ADC and D-ADC) we pooled sensitivity and specificity and calculated the area (AUC) under the summary receiver operating characteristics (sROC) curve. Results: We found 10 prospective and 8 retrospective studies examining correlation of ADC and CRT results. Overall, pCR rate was 25%. Pooled sensitivity, specificity, and AUC were: 0.743, 0.755, and 0.841 for pre-ADC; 0.745, 0.706, and 0.782 for post-ADC; and 0.832, 0.806, and 0.895 for D-ADC. Conclusions: Our meta-analysis confirms that at least 25% of patients with ARC experiences pCR after CRT. DW-MRI is a promising technique for assessment of CRT results and D-ADC appears to be the most effective parameter for prediction of pCR.