Finally, due the impact of the tyrosine kinase receptor pathway (e.g., IGF1R) on thyroid nodules and cancer, the possible impact of metformin on thyroid suspicious nodules and cancer should be investigated, especially in the light of a recent in-vitro evidence showing a down-regulation of oncogenic genes in human anaplastic thyroid cancer cells after incubation with metformin and pioglitazone [22]. This evidence concerns the gene NTRK1 and cancer.