RB1 and cancer: Palbociclib has been shown to be active in some cancers with CDKN2A loss, although impressive single agent efficacy is limited to case reports and it is in general primarily cytostatic.14 Preclinical data support the potential for benefit in cancers with Rb pathway alterations,15 but clinical trials in liposarcoma,16 ovarian cancer,17 nonsmall cell lung cancer,18 and colon cancer19 have demonstrated stable disease in a subset of patients with few tumour responses.