RB1 and retinoblastoma: GS-9876 treatment suppressed the proliferative response to pRB knockdown at all concentrations from 1.0 to 5.0 μM (Figure 10G), consistent with the notion that cone precursor intrinsic SYK activity contributes to the proliferative response to pRB loss and is retained in retinoblastoma cells (Figure 10H).