The molecular basis of their “oncogenic” role was clarified for the first time by our group in the context of prostate carcinoma cells, through the discovery of their target mRNA, p27kip1, a negative regulator of cell cycle progression [9], and then this same finding was confirmed in most forms of cancers where the overexpression of miR-221/222 had been detected [7], [8], [11], [13], [15]. Here, CDKN1B is linked to prostate carcinoma.