BMP4 and retinoblastoma: Interestingly, in RBL-15 cells (Fig D in S4 Fig), derived from a bilateral tumor, apoptosis induction by combined RA/BMP-4 treatment was considerably higher compared to the effects observed in Y-79 (Fig A in S4 Fig), RB355 (Fig B in S4 Fig) and RBL-30 (Fig C in S4 Fig), established from unilateral retinoblastomas, more or less mirroring the pro-apoptotic effects obtained in WERI-Rb1 cells.