Analysis of human MTC tissues from sporadic and hereditary cases showed that the cell cycle proteins, CDK2, cyclin-D1, p18INK4c, p19INK4d and p21CIP/WAF1 were consistently overexpressed in human sporadic, but not hereditary, forms of MTC (Table 1). The gene discussed is CCND1; the disease is medullary thyroid gland carcinoma.