- Arms A and B: Patients with hormone receptor positive disease must have had progressive disease and at least 2 lines of endocrine therapy, including one endocrine regimen used in combination with an approved CDK 4/6 (cyclin-dependent kinase ) inhibitor (eg, palbociclib). Relapse while receiving or within 6 months of completing adjuvant endocrine therapy may be considered failure of one prior endocrine regimen