## 4 Nanotechnology and Cancer
### Targeted Drug Delivery  
The field of nanotechnology for tumors has the potential to transform both cancer diagnostics and treatment [44]. Advances in protein engineering and material science have recently resulted in the creation of novel nanoscale targeting methods, providing renewed optimism for individuals dealing with breast cancer (BC) [45]. Moreover, nanoparticle therapy plays a role in reducing negative impacts on healthy tissues and organs [46]. Acknowledging its paradigm-shifting potential, the National Cancer Institute recognizes nanotechnology as an excellent strategy for advancing the diagnosis and therapy of breast cancer [42]. With positive clinical outcomes, numerous therapeutic nanoparticles have garnered approval and are extensively utilized in adjuvant therapy for breast cancer [47]. Drug delivery systems based on nanoparticles present a variety of designs determined by the shape, size, and composition of the biomaterials carrying the drugs [48]. These configurations enhance drug solubility, stability, circulatory half-life, biodistribution, and release rate while simultaneously reducing toxicity, immunogenicity, and side effects. Moreover, to precisely target breast cancer (BC) cells, targeting ligands can be incorporated onto the surface of nanoparticles (NPs), binding to the surface receptors of BC cells [49]. The modifiability of NPs is crucial for their effectiveness against cancer, overcoming drug resistance, and inhibiting metastasis [50]. NPs typically possess active or passive targeting capabilities, with sizes ranging from 1 to 100 nm, and their properties are dictated by the organic or inorganic coatings enveloping them. These properties not only decrease systemic toxicity in healthy tissues but also enhance drug concentration within the tumor [51]. Numerous studies have explored the advantages of NPs in drug delivery systems (DDSs) for BC therapy, emphasizing characteristics such as water dispersion, biocompatibility, biodegradability, stability, half-life in portal circulation, renal clearance, accumulation, and absorption [42]. Drug delivery systems (DDSs) are essential for comprehending the cellular and tissue-level responses of living systems to nanoparticles (NPs). Liposomes, exemplifying bilayered phospholipids, offer the capability to encapsulate both hydrophilic and hydrophobic medications [42; 52]. Customized liposomes demonstrate effective storage of medications until disruption, offering support for the sustained administration of drug formulations. Furthermore, they accumulate in cancer cells, enhancing drug selectivity and consequently reducing toxicity [53].  
The recent literature has delved into the progress of nanoparticle delivery systems designed for precise drug administration. Targeted delivery can be achieved through two approaches: active and passive. In active targeting, the medicinal substance or carrier system is bound to a ligand specific to a tissue or cell [54]. On the other hand, passive targeting involves incorporating the medicinal substance into a macromolecule or nanoparticle that naturally reaches the target organ [42]. Tumors can be passively targeted by nanoparticles containing the medicine or pharmaceuticals coupled to macromolecules via the Enhanced Permeability and Retention effect [42; 55]. Another method includes the use of catheters to directly infuse nanoparticles into the target organ or tissues [56]. For instance, localized administration of drug-laden nanoparticles to regions of vascular restenosis can facilitate prolonged drug release at specific areas of the arterial wall [42]. Refer to Figure 2 for a pictorial depiction of nanomaterials and carrier types employed as controlled therapeutic release systems.