SMAD3 is most highly expressed in the thyroid of all tissues analysed according to GTEx (see Supplementary Fig. 5), and the thyroid cancer risk alleles of the two variants associate with increased expression of SMAD3 in normal thyroid tissue, (rs56062135[T] has β=0.46 s.d., P=4.8 × 10−14, and rs2289261[C] has β=0.29 s.d., P=1.6 × 10−6). Here, SMAD3 is linked to thyroid cancer.