Our results show that homozygous deletion of the Patz1 gene worsens outcome in RET/PTC1 mice, since RET/PTC1TG;Patz1−/− mice develop thyroid carcinomas four months earlier than RET/PTC1TG;Patz1+/+ controls, and induces a thyroid cancer phenotype characterized by the presence of a higher number of proliferating cells and an increased incidence of the solid variant with respect to controls. The gene discussed is RET; the disease is thyroid gland carcinoma.