TG and thyroid tumor: In this regard, in vitro studies showed that Retinoids (Vitamin A-derived retinoic acids) are able to induce thyroid tumors redifferentiating effects like induction of 5′-deiodinase [47], increased expression of NIS mRNA [48], and increased thyroglobulin level (Tg), known to be lost in de-differentiated thyroid cancers [47].