INTERNATIONAL, MULTICENTER, RANDOMIZED, OPEN-LABEL, PHASE II CLINICAL TRIAL TO EVALUATE THE EFFICACY AND SAFETY OF CONTINUATION OF PALBOCICLIB IN COMBINATION WITH SECOND-LINE ENDOCRINE THERAPY IN HORMONE RECEPTOR-POSITIVE/HER2-NEGATIVE ADVANCED BREAST CANCER PATIENTS WHO HAVE ACHIEVED CLINICAL BENEFIT DURING FIRST-LINE PALBOCICLIB-BASED TREATMENT