Prognostic value of miR-21 in colorectal cancer, pancreatic ductal adenocarcinoma, and esophageal squamous cell carcinoma: updated systematic review and meta-analysis.

[OBJECTIVE] This study aims to conduct a systematic review of the prognostic value of miR-21 expression levels in patients with colorectal cancer (CRC), pancreatic ductal adenocarcinoma (PDAC), and esophageal squamous cell carcinoma (ESCC).

[METHODS AND RESULTS] We searched the PubMed, Embase, and CENTRAL databases for relevant studies published up to August 25, 2023. Sixteen studies, totaling 3096 patients, were included. High miR-21 expression was associated with higher hazard ratio (HR) values and decreased overall survival (OS) in CRC and PDAC, but this effect was not statistically significant in ESCC. The pooled HRs for CRC, PDAC, and ESCC were 1.54 (95% confidence interval [CI]: 1.14-2.07; P = 0.004; I2 = 71%), 2.11 (95% CI: 1.81-2.46; P < 0.001; I2 = 0%), and 1.79 (95% CI: 0.82-3.92; P = 0.15; I2 = 75%), respectively. Patients with high miR-21 expression had higher HR values and decreased disease-free survival (DFS) compared to those with low miR-21 expression in all three cancer types. The pooled HRs for CRC, PDAC, and ESCC were 1.88 (95% CI: 1.36-2.60; P < 0.001; I2 = 59%), 2.04 (95% CI: 1.34-3.11; P < 0.001; I2 = 17%), and 1.77 (95% CI: 1.04-3.03; P = 0.04; I2 = 36%), respectively.

[CONCLUSION] Elevated miR-21 expression levels are associated with poorer OS and DFS in patients with CRC, pancreatic cancer, and esophageal cancer. However, due to heterogeneity in the results, further large-sample, high-quality studies are needed to validate these findings.