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The incidence of thyroid cancer is increasing worldwide with the disease burden in Europe second only to that in Asia. In the last several decades, molecular pathways central to the pathogenesis of thyroid cancer have revealed a spectrum of targetable kinases/kinase receptors and oncogenic drivers characteristic of each histologic subtype, such as differentiated thyroid cancer, including papillary, follicular, and medullary thyroid cancer. Oncogenic alterations identified include B-Raf proto-oncogene (BRAF) fusions and mutations, neurotrophic tyrosine receptor kinase (NTRK) gene fusions, and rearranged during transfection (RET) receptor tyrosine kinase fusion and mutations. Multikinase inhibitors (MKIs) targeting RET in addition to multiple other kinases, such as sorafenib, lenvatinib and cabozantinib, have shown favourable activity in advanced radioiodine-refractory differentiated thyroid cancer or RET-altered medullary thyroid cancer; however, the clinical utility of MKI RET inhibition is limited by offtarget toxicity resulting in high rates of dose reduction and drug discontinuation. Newer and selective RET inhibitors, selpercatinib and pralsetinib, have demonstrated potent efficacy and favourable toxicity profiles in clinical trials in the treatment of RET-driven advanced thyroid cancer and are now a therapeutic option in some clinical settings. Importantly, the optimal benefits of available specific targeted treatments for advanced RET-driven thyroid cancer require genetic testing. Prior to the initiation of systemic therapy, and in treatment-naïve patients, RET inhibitors may be offered as first-line therapy if a RET alteration is found, supported by a multidisciplinary team approach. [ABSTRACT FROM AUTHOR]

Objective: Limited information is available on the incidence of rare thyroid cancer (TC) subtypes: anaplastic (ATC) and medullary (MTC). The aim of this study was to describe incidence variations and trends across European countries of all TC subtypes.Materials and Methods: We used the RARECAREnet database including 80721 TC incident cases in the period 2000-2007 from 77 population-based cancer registries (CRs) in Europe. In the trend analyses, we included 68890 TC cases from 53 CRs with at least 6 years of incidence data in the years 2000-2007.Results: In Europe age-standardised incidence rates (ASR) in women were <0.3/100,000 for MTC and ATC whereas ASR were 5.3/100,000 for papillary thyroid cancer (PTC) and 1.1/100,000 for follicular TC (FTC). Corresponding ASRs in men were <0.2/100,000 for MTC and ATC, 1.5 for PTC and 0.4 for FTC. Across countries and in both sexes the incidence of FTC and MTC was moderately correlated (r ~ 0.5) with that of PTC, while a less marked correlation (r < 0.4) emerged for ATC ASRs. The changes of the PTC ASRs across countries and time were weakly (r < 0.3) or moderately (r ~ 0.5) correlated to the changes of the other subtypes for both sexes.Conclusion: The huge increase and heterogeneity between countries of PTC incidence has a small influence on the trends and variations of MTC and ATC in Europe. Large-scale epidemiological and clinical registry-based studies are warranted to increase knowledge about the rarest TC subtypes. This information would be fundamental for the design of new clinical trials and for inference. [ABSTRACT FROM AUTHOR]