Of note, we should include here another rare scenario of the “hidden”, “forgotten”, or “missed” thyroid gland upon initial thyroidectomy, namely an ectopic thyroid tissue, particularly at the mediastinal level that might complicate the lifelong follow-up of a differentiated thyroid cancer via using serum thyroglobulin assays, which remains high due to the ectopic thyroid and might mimic a thyroid cancer recurrence [107,108,109,110]. This evidence concerns the gene TG and thyroid cancer.