RB1 and retinoblastoma: Retinoid X receptor gamma (RXRγ) [64] and thyroid hormone receptor beta 2 (TRβ2) [65,66], which are cone fate determinants, and M/L opsin are prominently produced in most retinoblastoma cells [46,48], agreeing with immunostaining of pRb-depleted cone cells of the normal retina [17] (Figure 1).