**5. Conclusions**

hypothermia have shown similar results regarding the reduction of intratumoral pressure as for irradiation [139]; ultrasounds due to mechanical (cavitation) and thermal pressure cause damage to tumor cells and ECM, which increase the interstitial hydraulic conductivity, reduces matrix tension and enhances tumor blood flow [140]; hyperbaric oxygen increases oxygen tension and delivery to tissues [141]; finally, photodynamic therapy impaired microcirculation in tumors [142]. All these strategies are possible by the knowledge of the physiopathology of vascularity in tumors ECM. Most of them are in the experimental phases and others are already

276 Composition and Function of the Extracellular Matrix in the Human Body

In the specific case of neuroblastic tumors, many relevant processes, such as stem cell differ‐ entiation, neuronal maturation, neurite extension, MYCN expression and the malignant potential and phenotype of tumor cells have all been shown to be influenced by ECM stiffness [1]. In this respect, our group performed a preliminary study where some differences regarding ECM elements could be described between favorable and unfavorable neuroblastic tumors [85]. This study was extended to a cohort of more than 500 samples where a stiffer, crosslinked and less porous ECM was mainly found in unfavorable tumors [143, 144]. Additionally, unfavorable tumors presented a highly vascularized ECM with mostly sinusoid vessels with abnormal morphologies [145]. Some ECM elements morphometric features helped the description of an ultra‐high risk subgroup which could beneficiate of novel therapies [146].

Cancer cells often express a variety of abnormal proteins that can serve as targets for an immune response. Although spontaneous immune responses to these antigens can occur, these reactions are rarely sufficient to cause tumor regression; however, the local administration of immune‐activating agents can induce tumor‐associated inflammation and protective immun‐ ity. By binding to their targets, antibodies exercise their functions through several effector mechanisms, including steric inhibition and neutralization, complement activation, and activation of cell‐mediated cytotoxicity. Each of these mechanisms may play a role in the antitumor activity of monoclonal antibodies; however, at present the relative importance of these mechanisms is not completely clear. In general, immune adjuvant–based therapies have only proven effective against early stage tumors; yet in this context they can be remarkably effective with minimal risk of serious adverse reactions [147]. Advances in immunotherapy have changed the management of several malignancies, being monoclonal antibodies the most specific targeted therapies currently in use [148]. Therefore, understanding how tumor cells develop immune escape mechanisms and create microenvironments that improve their survival and dissemination and to reach assay normalization seems crucial to achieving optimal treatment [69, 149, 150]. Most notable has been the ability of the anti‐CTLA4 antibody, ipilimumab, to achieve a significant increase in survival for patients with metastatic melanoma, for which conventional therapies have failed. In the context of advances in the understanding of how tolerance, immunity and immunosuppression regulate antitumor immune responses together with the advent of targeted therapies, suggesting that active immunotherapy represents a path to obtain a durable and long‐lasting response in cancer patients [151]. Five monoclonal antibodies are clinically approved for the treatment of hematologic tumors such as chronic lymphocytic leukemia (alemtuzumab), acute myelogenous leukemia (gemtuzu‐ mab), and non‐Hodgkin's lymphoma (rituximab, ibritumomab tiuxetan, and tositumomab)

in clinical trials.

In cancer biology, tumors are described as complex tissues comprised of heterogeneous neoplastic cells interwoven with tumor associated stroma. The characterization of the ECM elements associated with the tumoral and stromal cells presents opportunities for targeted therapeutic intervention. However, the heterogeneity of tumoral elements dictates that, in order to achieve successful clinical treatment, it is necessary to employ a combination of targeted therapies.

Novel and accurate image analysis algorithms must be developed and used to further investigate about tumor ECM composition and conformation and its relationship with different malignancies prognosis. Digital pathology approaches based on automated image analysis are necessary to obtain standardization, reproducibility, and eliminate observers' biases.

The definition of favorable and unfavorable ECM characteristics, together with the under‐ standing of the fact that biomechanical forces affect cell‐cell and cell‐matrix crosstalk and alter tumor cells fate, suggests the possibility of developing new therapies that can target the behaviors that arise from these complex interactions and from the heterogeneity of tumor tissues.
