The International Agency for Research on Cancer (IARC) has classified following viruses as carcinogens after comprehensive analysis: Epstein-Barr virus (EBV), hepatitis B virus (HBV), hepatitis C virus (HCV), Kaposi's sarcoma herpes virus (KSHV), human immunodeficiency virus, type-1 (HIV-1), human T cell lymphotropic virus, type-1 (HTLV-1), and human papillomavirus (HPV). EBV, HPV, HTLV-1, and KSHV are classified as direct carcinogens while HBV, HCV and HIV-1 are considered indirect carcinogens (HBV and HCV cause chronic inflammation and HIV-1 causes immune suppression). CRISPR/Cas technology has a promising role in targeting E6 or E7 genes in HPV, which are responsible for inducing cervical carcinoma. Kennedy et al. showed that the expression of a bacterial Cas9 RNA-guided endonuclease, together with sgRNAs specific for E6 or E7, induced cleavage of the HPV genome, resulting from inactivating mutations (deletions and insertions) into the E6 or E7 gene. This further induced p53 or retinoblastoma (Rb) protein, leading to cell cycle arrest and eventual cell death. In another study, CRISPR/Cas9 was used to target the promoter of HPV 16 E6/E7 as well as E6, E7 transcript resulting in significant reduction in proliferation of cervical cancer cell line SiHa and reduced tumorigenesis in mouse models. The CRISPR/Cas9 system could successfully treat EBV-related cancers during the latent phase of EBV infections by targeting EBV viral genomes. CRISPR/Cas9 was shown to cause direct cleavage of the JCV genome, a small circular dsDNA that encodes for the viral early protein, T-antigen. CRISPR/Cas9 was used to stop viral replication in transformed human glial cells because of the inactivation of the T-antigen-coding genes, which are critical for directing viral reactivation and lytic infection. The following two approaches are not direct therapy approaches but are important tools in translational research. They both help in understanding molecular mechanisms of various cancerous phenotypes providing invaluable information during early phases of drug discovery: