STAT3 and cancer: Since miR-21 has been shown to target cancer-relevant genes such as the phosphatase and tensin homolog (PTEN), programmed cell death protein 4 (PCDP4), reversion-inducing cysteine-rich protein with Kazal motifs (RECK) and signal transducer activator of transcription 3 (STAT3), it is involved in carcinogenic processes and might serve as a diagnostic and prognostic biomarker or as a therapeutic target for several cancer types [105].