Recent knowledge of the human genome and the application of molecular genetics to human biology have allowed new discoveries leading to a better understanding of how to diagnose and treat a variety of diseases. More recently, tremendous advances in molecular medicine, such as immunology, virology, genetics, and tumor biology, have generated considerable enthusiasm for gene therapy [1]. Cancers are genetic diseases that develop in a multistep process resulting from an accumulation of a series of genetic changes, such as mutations in DNA-repairing genes, in oncogenes, and tumor-suppressor genes which regulate normal cellular function in the genome of cells, causing alterations in the communication between cells [2, 3]. Breast cancer is one of the most important malignancies in women that accounts for 21 % of new cancer cases throughout the world [4, 5]. Five percent to 10 % of breast cancer has a genetic origin, i.e., hereditary, and 85–90 % of cases (known as sporadic or nonhereditary) have environmental origins that are yet to be understood [6, 7]. Conventional therapies, such as radiotherapy, chemotherapy, and hormonal therapy, have become more efficient for early detected cancers (Table 26.1). However, they are unable to cure the disease permanently and they still remain poor for advanced cancers. In parallel to these conventional therapies, gene therapy—a therapeutic strategy that embeds genes in cells or tissues of an individual to treat a disease—could be an alternative approach that can be used in the treatment of both genetic and acquired diseases [1, 9–11]. Even though the accessible and practicable vector systems for gene therapy can favorably transfer the genes into cells, the ideal delivery vehicle has not been found yet (Fig. 26.1). In this regard, many studies are ongoing to find more efficient viral and nonviral vector systems. Different therapeutic approaches can be considered when the molecular and pathophysiological basis of disease is disbanded. Pharmacological approach for which one can try to design a specific drug based on the functional properties of the deficient gene product or genetics for which manipulation based on the insertion of “transgenes” compensate the dysfunction of endogenous genes supporting the production of the deficient protein in cells where the anomaly is expressed. The prospects for this type of treatment can be applied to constitutional genetic diseases due to the alteration of a single gene or acquired diseases such as AIDS, cancer, thromboembolic disease, and cardiovascular disease or still some degenerative neurological diseases [12–14]. Insofar as the cancer is linked to the production of multiple mutations in a single cell that causes dysfunction of certain genes and the proliferation is out of control, a gene therapy permits to replace a defective gene responsible for disease by intact gene-encoding proteins. To this end, it can help prevent the action of proteins activating the uncontrolled proliferation of cells or restoring the functions of proteins that control cell division [10, 15]. Gene therapy is not a treatment, but it is one method of treatment. The principle is to “inject” a “normal” gene into a cell, in order either to replace a defective gene or to make a substance to destroy tumor cells, such as interleukin which is still experimental and cannot be prescribed outside clinical trials [16–18]. Cancer gene therapy is the transfer of nucleic acids which may be genes, portions of genes, oligonucleotides, or RNA into cancer or normal cells. Gene therapy for cancer includes different approaches, such as mutation correction, enhancement of the immune response against tumors, suicide gene, and antiangiogenic therapy to correct genetic errors or immunomodulation to reverse the malignant state [19].

Basically two types of gene therapy have been applied to humans, germinal and somatic:

For cancer gene therapy, broadly speaking there are three strategies which are used to achieve the goals of gene therapy: (1) in vitro/ex vivo, which initially involves removal of the patient’s target cells in order to culture in vitro and are then incubated for genetic modification with the viral vector carrying the therapeutic gene. The genetically altered cells are then reintroduced into the patient’s body. This method is used particularly with blood cells that are easy to remove and reinsert; (2) in situ consists of placing directly the transfer vector into the target tissue. This technique is used particularly in cases of cystic fibrosis (transfer vectors in the trachea and bronchi), muscular dystrophy (injection into the muscle of a vector carrying the gene for dystrophin), or cancer (tumor injection of a vector carrying the gene for a toxin); (3) in vivo involves injecting the vector carrying the therapeutic gene directly into the diseased cells of the organism via vectors and the vector is then supposed to reach specific target cells. But, of course, gene therapy is more difficult to achieve in vivo [13, 21].

Successful gene therapy requires decisions concerning the choice of suitable biological, chemical, and physical methods in order to modify the numbers of target cells necessary to obtain the desired therapeutic effect (Table 26.2).