MicroRNA expression can be regulated by different mechanisms such as chromosomal abnormalities, single nucleotide polymorphisms (SNPs), mutations in the primary transcripts such as miR-15a and miR-16-1 [156], altered activity of different transcription factors such as miR-17-92 cluster and changes in miR-34 family due to activation of p53. These mechanisms can be associated with different types of cancers such those of the bladder, lung and breast [156,157,158]. The gene discussed is TP53; the disease is cancer.