MiR-21 promotes CRC cell proliferation, invasion, and therapy resistance by targeting miR-21 functions by suppressing the expression of tumor suppressor genes such as programmed cell death 4 (PDCD4), tropomyosin 1 (TPM1), and phosphatase and tensin homolog (PTEN) genes, which normally act to restrain cancer progression [125]. Here, PDCD4 is linked to cancer.