THE COMPLEX RELATIONSHIP BETWEEN CHRONIC INFLAMMATION AND DIFFERENTIATED THYROID CANCER: EVIDENCE FROM IN VITRO AND CLINICAL STUDIES

Inflammation is an essential component of malignancies, including differentiated thyroid cancer (DTC). Thyroid cancer microenvironment is composed of a mixture of immune cells and soluble mediators. Among them, the chemokine CXCL8 exerts multiple pro-tumorigenic activities, including a chemotactic action on circulating neutrophils, induction of tumor cells growth, increase in angiogenesis and induction of the epithelial to mesenchymal transition, which promotes cell migration. Clinical studies in patients affected by several types of cancer evidenced that CXCL8 serum levels reflect the tumor burden and are related with the tumor aggressiveness. Solid evidence indicates that CXCL8 targeting can reduce tumor progression. The controversial relationship between inflammation and thyroid cancer tumorigenesis involves also the debated topic of the association between chronic-autoimmune-thyroiditis (CAT) and (DTC). DTCs are often diagnosed in the context of CAT and display an inflammatory-immune cells infiltration at histology, but whether the malignant transformation is promoted by the inflammatory response, or the peri-tumoral inflammation is induced by cancer-specific inflammatory molecules is still a matter of debate. This thesis project had two principal aims, i) to investigate the role of a pro-tumorigenic chemokine (CXCL8) in thyroid cancer microenvironment and to test in vitro the modulating properties of two different pharmacologic agents (PLX4720 and phenformin) and ii) to evaluate if CAT is a risk factor for the de novo development of DTC through a longitudinal population study. For Aim 1, thyroid cancer cell lines both BRAFV600E mutated (BCPAP, 8305C, 8505C) and RET/PTC rearranged (TPC-1), and normal human thyrocytes (NHT) were cultured alone or after treatment with two PLX4720 ore phenformin at increasing concentrations. CXCL8 concentrations were measured in the cell supernatants. Cell viability was evaluated through WST-1 and Annexin/propidium assay. Metastatic potential was assessed with migration assay and colony formation assay. For Aim 2, a retrospective longitudinal cohort study was designed including 510 CAT patients with a 10-years follow-up. The results of the first part of the thesis demonstrate that thyroid cancer cells secrete high amounts of CXCL8 and that both PLX4720 and phenformin are able to exert several anti-cancer activities within cancer microenvironment that are in part due to the inhibition of CXCL8 secretion. The results of the second part of the study indicate that the presence of CAT is not a risk factor for the new onset of DTC during long-term follow-up. The results of this thesis project suggest that two different kinds of inflammation (cancer-related and autoimmunity-related) exert different effects on DTC microenvironment and could have opposite effects on DTC development and prognosis.