In this light, we retrospectively evaluated seven variants belonging to cytochrome P450 (CYP3A4 rs2242480 and rs2687116 and CYP3A5 rs776746) genes and to ATP-binding cassette transporter (ABCB1 rs1045642, rs2032582 and rs2235048 and ABCG2 rs2231142) genes in a small group of advanced thyroid cancer patients treated with lenvatinib to study the possible correlation between polymorphisms (SNPs), outcome and the appearance of drug-related AEs. This evidence concerns the gene CYP3A4 and thyroid gland carcinoma.