ADC as a predictor of pathologic response to neoadjuvant therapy in esophageal cancer: a systematic review and meta-analysis

Objective Diffusion-weighted magnetic resonance imaging (DWI) is part of clinical practice. The aim of this study was to evaluate the role of apparent diffusion coefficient (ADC) as a predictor of pathologic response to neoadjuvant therapy (nCRT) in patients with esophageal cancer (EC). Methods The MEDLINE, Embase, and Google Scholar databases were systematically searched for studies using ADC to evaluate response to neoadjuvant therapy in patients with EC. Methodological quality of the studies was evaluated with the QUADAS tool. Data from eligible studies were extracted and evaluated by two independent reviewers. Meta-analyses were performed comparing mean ADC values between responders and non-responders to nCRT in three different scenarios: baseline (BL) absolute values; percent change between intermediate (IM) values and BL; and percent change between final follow-up (FU) value and baseline BL. Results Seven studies (n = 158 patients) were included. Responders exhibited a statistically significant percent increase in ADC during nCRT (mean difference [MD] 21.06%, 95%CI = 13.04-29.09;I-2 = 49%;p = 0.12). A similar increase was identified in the complete pathologic response (pCR) versus non-complete pathologic response (npCR) subgroup (MD = 25.68%, 95%CI = 18.87-32.48;I-2 = 0%;p = 0.60). At the end of treatment, responders also exhibited a statistically significant percent increase in ADC (MD = 22.49%, 95%CI = 9.94-35.05;I-2 = 0%;p = 0.46). BL ADC was not associated with any definition of pathologic response (MD = 0.11%, 95%CI = - 0.21-0.42;I-2 = 85%;p < 0.01). Conclusion These results suggest that ADC can be used as a predictor of pathologic response, with a statistically significant association between percent ADC increase during and after treatment and pCR. ADC may serve as a tool to help in guiding clinical decisions.