Mice heterozygous for Rb generate thyroid medullary cancer (MTC) from calcitonin-producing neuroendocrine cells as a consequence of biallelic loss of Rb. We reported that thyroid medullary cancer derived from calcitonin-producing cells as a consequence of biallelic loss of Rb; these cells exhibit dedifferentiated characteristics, depicted by a lower expression of calcitonin in a Trp53-null but not in genetic backgrounds lacking other p53 pathway genes, such as Arf and Cdkn1a [38]. The gene discussed is CDKN2A; the disease is medullary thyroid gland carcinoma.