Bacteria have spacer sequences of deoxyribonucleic acid that resemble genomic sequences of phage viruses between repetitive DNA sequences known as CRISPR. A CRISPR and spacer DNA template can be used to create transactivating tracrRNAs and targeting crRNAs that cleave DNA complementary to the crRNA, allowing the system to be engineered for cleaving any desired DNA sequence. In genetic engineering, it has revolutionalized the field of medicine in treating various genetically-linked diseases that are difficult to treat such as Leber congenital amaurosis, retinitis pigmentosa, open angle glaucoma, haemophilia B, sickle cell disease or thalassemia, Duchenne muscular dystrophy, and malignancies such as malignant rhabdoid tumours. The CRISPR/Cas9 method has successfully accelerated and simplified editing of genes in CAR T cells with CD19-specific anti-tumor activity in malignancies such as lymphoma, malignant rhabdoid tumours and other embryonal tumours of the brain. The addition of small molecules as perturbations, functional genome screening with the CRISPR system could help to investigate interactions between genes and drugs, reveal changes in expression of genes following cancer drug therapy, and identify novel targets for precise treatment, while also shedding light on the genesis of disease, thereby making CRISPR-Cas technology, a recent tool, which is highly beneficial in theranostics.