RB1 and retinoblastoma: pRB-positive cells were observed in the eye section of an 8-week-old human embryo in the retina and choroids (Figure 6a), in retinoblastoma (retina and tumor tissue) (Figure 6b), and in various types of melanomas (retina, choroids, and tumor tissue) (Figure 6d), with the exception of epithelioid melanoma, which had no pRB expression in the choroids.