We knocked out TET1 in thyroid cancer cell line C643 using the lentivirus-mediated CRISPR-Cas9 system and successfully validated TET1 knockout in single-cell colonies by Sanger sequencing, western blot analysis and dot-blot analysis of genomic 5-hmC (Supplementary Table 1 and Fig. 2E). The gene discussed is TET1; the disease is thyroid gland carcinoma.