For example, CRISPR has been applied to breast cancer diagnosis, treatment, and even drug resistance research.18 Based on the CRISPR-dCas9 system, researchers have fused a DNA methyltransferase effector to dCas9 and infected it by lentivirus into healthy breast cells.19 The results showed that the cyclin dependent kinase inhibitor 2A (CDKN2A) gene is a key driver in causing abnormally rapid cell division, which might be an early diagnostic marker in breast cancer. The gene discussed is CDKN2A; the disease is breast cancer.