Earlier studies shown that miR-21 gave BC cells a strong proliferative capacity, a low rate of apoptosis, and a high capacity for invasion and for this reason, Gao and coworkers revealed that delivery of anti-miR-21 with poly(L-lysine)-modified PEI complex (PEI-PLL) to breast cancer cells resulted in an increase in G1 cell cycle arrest and elevated caspase-3 expression, which caused apoptosis [242]. Here, CASP3 is linked to breast cancer.