**4.3 miRNAs in treatment response prediction of colorectal cancer**

A variety of therapeutic advances are existed for CRC treatment such as conventional chemotherapy (5-fluorouracil, capecitabine, irinotecan, oxaliplatin), immunotherapy, radiotherapy, and chemoradiotherapy. miRNAs play an important role in the regulation of effectiveness and resistance to these therapies and prediction of personalized therapy response [84, 85]. Resistance to therapy is still the biggest challenge for defeating cancer. It may be caused by a variety of reasons such as reduction in transportation and intracellular accumulation of drugs by modulating the activity of drug transporters such ATP-binding cassette subfamily B (ABCB)/multidrug resistance (MDR) transporters (which is reviewed in reference [86]), dysregulation in DNA damage repair mechanisms, insufficient or oncogenic immune response, blockage of apoptosis, emergence of inflammation, and altered expression of oncogenes and tumor suppressor genes related with therapy response. miRNAs are actively participating in all of these resistance mechanisms [87, 88].
