Breast cancer is the most common type of neoplasia in women. Most of hereditary cases are associated with mutations of breast cancer-associated genes (BRCA). Preventive mastectomy and chemoprevention are the only approaches available so far to prevent the development of neoplasia in patients with specific genetic background. However, side effects and invasiveness of these procedures make necessary the development of alternative strategies. This book describes a novel approach to prevent breast cancer based on the restoration of BRCA1 functional gene into target cells using an engineered virus. In fact viruses have developed an efficient mechanism to deliver their genetic material into target cells; virus-derived vectors take advantages of this ability to vehiculate transgenes cells. To this aim a lentiviral vector expressing BRCA1 gene was produced. Restoration of gene function was validated in tumor and primary cells derived from patient encoding an inactive form of BRCA1, that, following gene delivery, restored the ability to repair DNA damages upon exposition to ionizing radiations These results pave the way to develop novel preventative approaches against human breast cancer.