Pretreatment apparent diffusion coefficient cannot predict histopathological features and response to neoadjuvant radiochemotherapy in rectal cancer. A Meta-Analysis.

AIM: Our purpose was to perform a systemic literature review and meta-analysis regarding use of apparent diffusion coefficient (ADC) for prediction of histopathological features in rectal cancer (RC) and to proof if ADC can predict treatment response to neoadjivant radiochemotherapy in RC. METHODS: MEDLINE library, Cochrane and SCOPUS database were screened for associations between ADC and histopathology and/or treatment response in RC up to June 2020. Authors, year of publication, study design, number of patients, mean value and standard deviation of ADC were acquired. The methodological quality of the collected studies was checked according to the QUADAS 2 instrument. The meta-analysis was undertaken by using RevMan 5.3 software. DerSimonian and Laird random-effects models with inverse-variance weights were used to account the heterogeneity between the studies. Mean ADC values including 95% confidence intervals were calculated. RESULTS: Overall, 37 items (2015 patients) were included. ADC values of tumors with different T and N stages and grades overlapped strongly. ADC cannot distinguish RC with high and low CEA level. Regarding KRAS status, ADC cannot discriminate mutated and wild type RC. ADC did not correlate significantly with expression of VEGF and HIF 1a. ADC correlates with Ki 67, calculated correlation coefficient: -0.52. The ADC values in responders and non-responders overlapped significantly. CONCLUSION: ADC correlates moderately with expression of Ki 67 in RC. ADC cannot discriminate tumor stages, grades and KRAS status in RC. ADC cannot predict therapy response to neoadjuvant radiochemotherapy in RC.