ESR1 and thyroid cancer: When approached during pregnancy, the optimal indication for surgery is the second trimester, since there is a teratogenic risk in the first trimester and a risk of early delivery in the third trimester.6, 15 The decision to operate during pregnancy is associated with the effects of human Chorionic Gonadotropin (hCG) on nodule growth due to reactivity of hCG with the TSH receptor.14, 16 More recent studies have also indicated that most of thyroid cancers in pregnancy present Estrogen Receptors alpha (ER-α), and their growth is therefore stimulated by high estrogen levels.17