p19-positive cells were observed in the eye section of an 8-week-old human embryo in the retina and choroid (Figure 2a), in retinoblastoma (unaffected retina, choroid, and tumor tissue) (Figure 2b), in the retina of the normal human eye (Figure 2c), and in various types of melanomas (retina, choroid, and tumor tissue) (Figure 2d). Here, CDKN2A is linked to retinoblastoma.