TG and neoplasm: Another aspect for consideration during the follow-up of patients with PTC is the interpretation of serum Tg (sTg) values in the presence of serum anti-Tg antibodies (sTgAb), which occurs in approximately 25% of patients with PTC; these antibodies may interfere with the measurement of sTg, which compromises the use of this tumor marker in the follow-up of patients with PTC (24).