Palbociclib is also being assessed as part of a multi-arm phase 2 basket study involving multiple tumor subtypes, including patients with mCRPC who would be eligible for palbociclib if they have CCND1, -2, -3, or CDK4/6 amplification with retained Rb expression by IHC with a planned primary outcome of ORR (NCT02465060). Here, RB1 is linked to neoplasm.