Rare thyroid malignancies in Europe: Data from the information network on rare cancers in Europe (RARECAREnet)

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.