Mohadeseh Khoshandam - Department of Reproductive Biology, Academic Center for Education,Culture, and Research (ACECR), Qom branch ۳۷۱۶۹۸۶۴۶۶,Iran. National institute of genetic engineering and biotechnology(NIGEB), Tehran ۱۴۹۶۵/۱۶۱, Iran.
Hossein Soltaninejad - Faculty of Interdisciplinary Science and Technology, TarbiatModares University, Tehran ۱۵۶۱۴, Iran ۴- Pediatric Cell Therapyand Gene Therapy Research Center, Gene, Cell & Tissue ResearchInstitute, Tehran University of Medical Sciences, Tehran۱۴۱۷۹۳۵۸۴۰, I
Saman Hosseinkhani - Department of Biochemistry, Faculty of Biological Sciences, TarbiatModares University, Tehran ۱۵۶۱۴, Iran

Background: Breast cancer (BC) is the most common type ofcancer in women worldwide, accounting for about ۲۸% of newcancers. The accumulation of genetic lesions, aberrant gene expressionand protein degradation are considered as the basis forthe initiation of tumor formation and metastasis. Therefore, itis challenging to identify genes and molecules that can potentiallybe used as potent biomarkers for personalized medicinewith minimal or no side effect. The CRISPR-cas۹ system is apowerful tool for gene editing and is useful for searching forsynergistic killer or tumor-driven genes with the aim of overcoming drug resistance as a personalized treatment method andremoving treatment limitations.Materials and Methods: In this review article, ۱۸۲ valid articlesfrom PubMed and Google Scholar databases were used ,and the best articles were selected. Search keywords are CRISPR-cas۹, breast cancer, gene therapy, precision medicine. Thisreview article examines the use of CRISPR-cas۹ for precisionmedicine in the treatment of breast cancer.Results: The use of the CRISPR/Cas۹ system provides a rapidapproach for targeted modification of endogenous loci andovercomes the limitations of other methods. But there are stillseveral factors for the full clinical application of CRISPR/Cas۹in terms of efficacy and safety, such as suitability of modifiedcells, editing efficiency, delivery methods and potential offtargeteffects. Edited cells often have fitness defects, such asreduced ability to proliferate and differentiate, leading to insufficienttherapeutic effects. On the other hand, cancer cellshave advantages in terms of growth, including rapid proliferationand long survival. This requires high editing efficiency forCRISPR-Cas۹.Conclusion: Personalized cancer medicine is still being developedby researchers, and CRISPR-Cas۹ is still in the earlystages of research. All the challenges in genome editing must besolved before implementation in humans. However, CRISPR/Cas۹ has been used on human cancer cells such as melanomaand prostate cancer, and has also been tested in non-small celllung cancers, leukemia and lymphoma. Genome editing inpersonalized cancer treatment is likely to revolutionize cancertreatment in the future.

CRISPR-cas۹, breast cancer, Gene therapy, precisionmedicine