Context:Genome-wide association studies (GWASs) of differentiated thyroid cancer (DTC) have identified associations with polymorphisms at 2q35 (DIRC3), 8p12 (NRG1), 9q22.33 (FOXE1) and 14q13.2 (NKX2-1). However, most of the inherited genetic risk factors of DTC remain to be discovered.Objective:Our objective was to identify additional common DTC susceptibility loci.Design:We conducted a GWAS in a high-incidence Italian population of 690 cases and 497 controls and followed up the most significant polymorphisms in two additional Italian series and in three low-incidence populations totaling 2,958 cases and 3,727 controls.Results:After excluding the most robust previously identified locus (9q22.33), the strongest association was shown by rs6759952 confirming the recently published association in DIRC3 (OR = 1.21, P = 6.4 × 10(-10), GWAS and all replications combined). Additionally, in the combined analysis of the Italian series, suggestive associations were attained with rs10238549 and rs7800391 in IMMP2L (OR = 1.27, P = 4.1 × 10(-6) and OR = 1.25, P = 5.7 × 10(-6)), rs7617304 in RARRES1 (OR =1.25, P = 4.6 × 10(-5)) and rs10781500 in SNAPC4/CARD9 (OR = 1.23, P = 3.5 × 10(-5)).Conclusions:Our findings provide further insights into the genetic and biological basis of inherited genetic susceptibility to DTC. Further studies are needed to determine the role of the identified polymorphisms in the development of DTC and their possible use in the clinical practice.