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 similar to 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 similar to 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.