Retinoblastoma is a type of cancer that occurs early in child development. This disease is rare, with only 1 out of 20,000 children affected (Genes and Disease). Why study such a rare disease? Metastatic retinoblastoma is among the most deadly of childhood cancers with a less than 10% probability of survival. Secondly, studies in retinoblastoma have paved the way for understanding many of the molecular interactions that drive tumorigenesis in other tissues. Retinoblastoma is associated with mutations of the Rb gene locus. Rb is a tumor suppressor gene, which functions to regulate the cell cycle, and mutations of the Rb locus can lead to cell proliferation. The Rb protein regulates the cell cycle by binding to the E2F transcription factor. The E2F transcription factor is involved with cell cycle progression (proliferation) but also has a key role in programmed cell death, also known as apoptosis (Hallstrom). Understanding how mutations of the Rb locus is involved with cell proliferation will likely be useful for diagnosis and pharmacological treatment of many cancer types.