**5. Conclusions & future**

Cancer is a complex disease with a plethora of cell types and differentiation stages that trigger standard molecular mechanisms towards recruitment of cells and nutrients to enhance survival and proliferation. Cancer complexity is also dependent from the specific and multi‐ faceted umor microenvironment. All these different molecular pathways, mechanism and markers can be used as potential targets for therapeutics. However, current therapeutics (drugs and molecules) show serious cell toxicity that is not merely directed at the cancer cells but instead promote off-target cellular disarray and cell death, usually reported ad undesirable side effects and systemic toxicity.

Nanomedicine has been putting forward several therapeutic concepts that disrupt the way we have been dealing with cancer therapy, i.e. nanoparticles as drug delivery agents, minimising side effects and toxicity of the drugs. Furthermore, these nanoparticle platforms allow for selective targeting of cancer cells or tumor vessels either by incorporating novel or standard anticancer drugs and/or the delivery of therapeutic genetic modulators. These approaches, often based on the robustness and chemical properties of AuNPs, have shown great promise in preclinical models. Some recent advances in ligand-targeted NPs have begun to demonstrate improvement in cancer therapy.

What is more, many tumors become resistant to drugs, requiring that novel strategies involv‐ ing drug targeting vehicles that deliver high concentrations of combinatorial therapeutics to the selected targets. For this to happen, it is crucial that these nanoconjugates are capable to withstand the body's clearance and reaction to non-self particulates. The robustness of AuNPs as target delivery platforms will be achieved when reticuloendothelial system clearance is avoid and occur an enhance of the endothelial penetration, once the first one can lead to a longer time in circulation and the second leads to an increase of targeting and drug accumu‐ lation (Kumar *et al.*, 2013).

The use of multiple nanoparticles that can be used together may overcome current limitations of each individual nanoformulation alone. For example, AuNPs have proven to be outstanding vectorisation systems for gene delivery and can be used to target molecular pathways, including those involved in drug resistance and in survival of cancer cells. These NPs may be used in combination with any other polymeric and/or metallic nanoparticles in therapeutic approaches that include drug and thermal ablation, selective delivery via out of the boy triggering (light source).

All of these applications of AuNPs in therapeutics still lack enough toxicology and pharma‐ cology studies and data that can support the effective translation into the clinics. However, the efficacy in fighting cancer cells shows that the effort to push forward with the needed regulatory requirements and compliance is worth pursuing since the enhanced properties allow for outstanding improvements to biocompatibility, circulation and therapeutic response.
