en Prevention, Early Detection and Screening Letters to the Editor <div style="text-align: justify;"><span style="font-size:11pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="font-size:10.5pt"><span style="line-height:120%"><span style="color:#231f20">MicroRNA‑21 (miR‑21) is frequently upregulated in colorectal cancer (CRC) and has been associated with tumor progression and poor prognosis. However, its clinical and biological roles remain complex and context‑dependent. Evidence indicates that miR‑21 is dysregulated in multiple diseases, limiting its specificity as a standalone diagnostic biomarker for CRC. Moreover, recent studies suggest that miR‑21 participates in diverse processes including modulation of inflammatory signaling, remodeling of the tumor microenvironment, immune regulation, and chemotherapy resistance. Despite promising experimental findings, therapeutic targeting of miR‑21 has not yet progressed to clinical trials due to challenges in delivery and specificity. Future studies using advanced models such as CRISPR‑based gene editing and patient‑derived organoids may clarify the functional significance of miR‑21 and determine its potential as a clinically actionable target in CRC.</span></span></span><span style="font-size:10.5pt"><span style="line-height:120%"></span></span></span></span></span></div> MicroRNA 21 (miR 21), colorectal cancer (CRC), chemotherapy 0 0 http://mcijournal.com/browse.php?a_code=A-10-682-1&slc_lang=en&sid=1 Maryam Fazeli fazelim9@gmail.com 10031947532846004278 10031947532846004278 No Advanced Therapy Medicinal Product (ATMP) Department, National Cancer Institute, Academic Center for Education, Culture and Research (ACECR), Tehran, Iran behzad Pourhossein pourhossein.b@sbmu.ac.ir 10031947532846004279 10031947532846004279 Yes Pharmaceutical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran