miR-21 is an oncomiR, directly targeting several tumor suppressor genes, increasing the aggressiveness of tumor cells such as PTEN [65], programmed cell death 4 (PDCD4), a negative regulator of nuclear factor kappa B (NF-kB; an essential transcription factor involved in the regulation of immune checkpoint expression) [67,68] and signal transducer and activator of transcription 1 (STAT1), which is involved in M1-macrophage polarization. This evidence concerns the gene PDCD4 and neoplasm.