The experimental approaches based on this multipurpose technology

The prokaryotic type II clustered regularly interspaced short
palindromic repeats (CRISPR)-Cas9 system is rapidly revolutionizing the genetic
engineering field, altering the genomes of large varieties of organisms with
relative ease. Cancer genetics can be changed using experimental approaches based
on this multipurpose technology 1. Principal component of the Type II CRISPR/Cas system is the
Cas9 endonuclease, a prokaryotic adaptive restriction system against invading
nucleic acids, such as those of bacteriophages and plasmids. Recently, this
RNA-directed DNA endonuclease has been coupled to target DNA sequences of
interest. Through guidance of a 20 nucleotide RNA (gRNA),
CRISPR-Cas9 finds and cuts target protospacer DNA precisely 3 base pairs
upstream of a PAM (Protospacer Adjacent Motif) 
2. Cas9 not only edits the genomes of a number of
different prokaryotic and eukaryotic species, but also an efficient system for
site-specific transcriptional repression or activation 3. It can modify any genomic sequences, thereby
providing a specific, simple, easy, and cost effective means of genome wide
gene editing, analogous to the search function in modern word processors, Cas9
can be guided to specific locations within complex genomes by a short RNA
search string. Cas9-mediated genetic perturbation is simple and accessible, exposing
the functional organization of the genome at the systems level and establishing
causal linkages between genetic variations and biological phenotypes 4 As a RNA-guided
DNA recognition platform, it permits precise, scalable and robust RNA-guided
transcription regulation 5, in contrast to RNA-mediated
interference (RNAi), that uses small interfering RNAs (siRNAs) or short hairpin
RNAs (shRNAs), that act as sequence-specific gene suppression in eukaryotic
organisms 6 but also non-specific
and inefficient 7. Genome engineering via RNA-guided CRISPR-Cas9 system
provides a novel methodology, to induce genomic modifications under the
endogenous gene promoters 8. During the last few years, the clustered regularly
interspaced short palindromic repeats (CRISPR) and the associated Cas9
nucleases (CRISPR-Cas9) have modernized the choices for targeted genome editing
9. These programmable RNA-guided
endonucleases (RGENs) comprise two RNA elements, CRISPR RNA (cRNA) and its
transactivating RNA (tracRNA), which fused together and induce a targeted
double-strand break (DSB),providing a corresponding DNA template, any specific
gene sequence can be introduced via homologous recombination (HR) 10.