It was found that treatment of ZnO NPs with dosages of 5, 10, and 20 μM/mL for 48 h led to a significant decrease in cancer cell viability and also caused a concentration-dependent elevation in mRNA expression and protein level of p53 and Bax, while reducing the expression of Bcl-2 and ER-α [75]. The gene discussed is BAX; the disease is cancer.