RB1 and retinoblastoma: Although previous studies have revealed the genetic backgrounds of certain types of cancer—for example, the MSH2 gene in familial nonpolyposis colon cancer [58], the BRCA1 gene in familial breast cancer [59]–[61], the APC gene in hereditary adenomatous polyposis [62], [63], and the RB gene in retinoblastoma [64], [65]—the functional mechanisms leading to cancer initiation, progression and development remain to be elucidated.