PFS is defined as the time from the date of randomization to the date of the first documentation of objective tumor progression as per Response Evaluation Criteria In Solid Tumors Criteria (RECIST v1.1) or death due to any cause in the absence of documented PD, whichever occurs first. If tumor progression data include more than 1 date, the first date will be used. PFS (in months) will be calculated as (first event date - randomization date +1)/30.4. Progression is defined using RECIST v1.1, as a 20% increase in the sum of diameters of target measurable lesions above the smallest sum observed (over baseline if no decrease in the sum is observed during therapy), with a minimum absolute increase of 5 mm, or unequivocal progression of pre-existing non-target lesions, or the appearance of new lesions.

ITT population or full analysis set included all participants who were randomized, with study drug assignment designated according to initial randomization, regardless of whether participants received study medication or received a different drug from that to which they were randomized.

Objective Response (OR) defined as overall complete response (CR) or partial response (PR) according to RECIST v1.1. Objective Response Rate (ORR) is defined as proportion of participants with CR or PR relative to all randomized participants with measurable disease at baseline. Participants who do not have on-study radiographic tumor re-evaluation, who received anti-tumor treatment, or who died, progressed/ dropped out for any reason prior to reaching a CR or PR were counted as non-responders in assessment of ORR. Per RECIST v1.1, CR: Complete disappearance of target lesions with exception of nodal disease. All target nodes must decrease to normal size (short axis <10mm). PR: >=30% decrease under baseline of the sum of diameters of all target measurable lesions. The short diameter is used in the sum for target nodes, while the longest diameter is used in the sum for all other target lesions. Stable Disease: neither sufficient shrinkage nor increase to qualify for disease progression.

ITT population or full analysis set included all participants who were randomized, with study medication, regardless of whether participants received study medication or received a different drug from that to which they were randomized.

The OR is defined as the overall CR or PR according to the RECIST v1.1. ORR is defined as proportion of participants with CR or PR relative to all randomized participants with measurable disease at baseline. Participants who do not have on-study radiographic tumor re-evaluation, who received anti-tumor treatment, or who died, progressed/ dropped out for any reason prior to reaching a CR or PR were counted as non-responders in the assessment of ORR. Per RECIST v1.1, CR: Complete disappearance of target lesions with exception of nodal disease. All target nodes must decrease to normal size (short axis <10mm). PR: >=30% decrease under baseline of the sum of diameters of all target measurable lesions. The short diameter is used in the sum for target nodes, while the longest diameter is used in the sum for all other target lesions. Stable Disease: neither sufficient shrinkage nor increase to qualify for disease progression.

Participants who had measurable disease at baseline.

DR is defined as the time from the first documentation of objective tumor response (CR or PR) to the first documentation of disease progression or to death due to any cause, whichever occurs first. If tumor progression data included more than 1 date, the first date will be used. DR was calculated as [the date response ended (i.e. date of PD or death) - first CR or PR date + 1)]/30.4. DR would only be calculated for the subgroup of participants with an objective tumor response. Per RECIST v1.1, CR: Complete disappearance of target lesions with exception of nodal disease. All target nodes must decrease to normal size (short axis <10mm). PR: >=30% decrease under baseline of the sum of diameters of all target measurable lesions.The short diameter is used in the sum for target nodes, while the longest diameter is used in the sum for all other target lesions. Stable Disease: neither sufficient shrinkage nor increase to qualify for disease progression.

Participants who had tumor response with CR or PR during study.

DC is defined as overall CR, PR, or stable disease (SD) >=24 weeks according to RECIST version 1.1. Disease Control Rate (DCR) is defined as participants with CR, PR, or SD >=24 weeks relative to all randomized participants. Participants who do not have on-study radiographic tumor reevaluation, who received anti-tumor treatment, a best response of SD>=24 weeks, or who died, progressed, or dropped out for any reason prior to achieving reaching a CR or PR and a best response of SD>=24 weeks was counted as non-responders in DCR. Per RECIST v1.1, CR: Complete disappearance of target lesions with exception of nodal disease. All target nodes must decrease to normal size (short axis <10mm). PR: >=30% decrease under baseline of the sum of diameters of all target measurable lesions. The short diameter is used in the sum for target nodes, while the longest diameter is used in the sum for all other target lesions. SD: neither sufficient shrinkage nor increase to qualify for disease progression.

ITT population or full analysis set included all participants who were randomized, with study medication, regardless of whether participants received study medication or received a different drug from that to which they were randomized.

PFS by biomarker status by Investigator assessment. Progression is defined using RECIST v1.1, as a 20% increase in the sum of the longest diameter of target lesions, or a measurable increase in a non-target lesion, or the appearance of new lesions. Positive is defined as H-Score >=1 and negative as H-Score <1. H-Score is calculated as the sum of the % of cells at each level of staining intensity (0, 1+, 2+, and 3+) multiplied by the staining intensity value: H-Score = (% at 0)*0 + (% at 1+)*1 + (% at 2+)*2 + (% at 3+)*3. H-Score values range from 0 to 300. ER stands for estrogen receptor and Rb stands for retinoblastoma susceptibility gene product.

ITT population or full analysis set included all participants who were randomized, with study medication, regardless of whether participants received study medication or received a different drug from that to which they were randomized. Here "Number Analyzed" signifies number of participants evaluable for specified rows.

Triplicate 12-lead ECG measurements (each recording separated by approximately 2 minutes) were performed and sent to a central laboratory for blinded manual adjudication. The average was calculated. The time corresponding to beginning of depolarization to repolarization of the ventricles (QT interval) was adjusted for RR interval using QT and RR from each ECG by Fridericia's formula (QTcF = QT divided by cube root of RR), by Bazette's formula (QTcB = QT divided by square root of RR) and corrected QT interval according to study-specific criteria (QTcS). Time-matched change from baseline values were reported for QTc analysis population.

QTc analysis set is a subset of as treated (AT) population who were in Group 1; their QTc was used to study the effect of palbociclib on QT interval via serial triplicate ECGs with PK draws; and who had >= 1 pair of time-matched Day 0 and palbociclib postdose (Cycle1 Day14) measurements.

Triplicate 12-lead ECG measurements (each recording separated by approximately 2 minutes) were performed and sent to a central laboratory for blinded manual adjudication. The average was calculated. The time corresponding to beginning of depolarization to repolarization of the ventricles (QT interval) was adjusted for RR interval using QT and RR from each ECG by Fridericia's formula (QTcF = QT divided by cube root of RR), by Bazette's formula (QTcB = QT divided by square root of RR) and corrected QT interval according to study-specific criteria (QTcS). Percentage of participants with post-baseline maximum absolute values and maximum increase from baseline were summarized for the safety analysis population.

The AT population or safety analysis set included all participants who received at least 1 dose of study medication, with treatment assignments designated according to actual study treatment received.

Summary of plasma palbociclib within-participant mean steady-state trough concentrations.

Pharmacokinetic analysis set was a subset of AT participants, who were treated with Palbociclib and had at least one measured plasma concentration. Here "Number Analyzed" signifies number of participants evaluable for specified rows.

The EuroQol EQ-5D is a 6-item instrument designed to assess health status in terms of a single index value or utility score. It contains 5 descriptors of current health state (mobility, self-care, usual activities, pain or discomfort, and anxiety or depression) with each dimension having 3 levels of function (1=no problem, 2=some problem, and 3=extreme problem). The scores on the 5 descriptors are summarized to create a single summary score. An overall utility score is calculated based on these domains, with a range score from 0 (worse health scenario) to a maximum of 1.0 (best health scenario).

Patient Reported Outcome (PRO) Analysis Set is a subset of ITT participants, who had both baseline and at least one follow-up PRO assessment.

FACT is a modular approach to assess participant health-related quality of life using a 'core' set of questions (FACT-G) as well as a cancer site-specific module. The FACT-G is a 27-item compilation of general questions divided into 4 domains: Physical Well-Being, Social/Family Well-Being, Emotional Well-Being, and Functional Well-Being. The FACT-B consisted of the FACT-G (27-item) and a breast-specific module: a 10-item instrument designed to assess participant concerns relating to breast cancer. For all questions, participants were asked to respond to a five-level scale where 0=not at all, 1=a little bit, 2=somewhat, 3=quite a bit, and 4=very much. FACT-B total score = Physical Well-Being + Social/Family Well-Being + Emotional Well-Being + Functional Well-Being + Breast Cancer Subscale. As each of the items ranges from 0-4, the range of possible scores is 0-144, with 0 being the worst possible score and 144 the best.

Patient Reported Outcome (PRO) Analysis Set is a subset of ITT participants, who had both baseline and at least one follow-up PRO assessment.

An AE was any untoward medical occurrence in a clinical investigation participant administered a product or medical device; the event need not necessarily have a causal relationship with the treatment or usage. SAE was any untoward medical occurrence at any dose that resulted in death; was life-threatening; required hospitalization; resulted in persistent or significant disability or in congenital anomaly/birth defect. TEAE were events that occurred between first dose of study drug and up to 28 days after last dose that were absent before treatment or that worsened relative to pretreatment state. Severity was graded by the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE), Version 4.0 as Grade 1 = mild, Grade 2 = moderate, Grade 3 = severe, Grade 4 = life-threatening and Grade 5 = death related to AE. Discontinuation included permanent, temporary discontinuation and dose reduction due to AEs.

AT population included all participants who received at least 1 dose of study medication, with treatment assignments designated according to actual study treatment received.

OS was defined as the time from date of randomization to date of death due to any cause. Participants without survival data beyond the date of their last follow-up were censored on the last date they were known to be alive. Data for this outcome measure was reported at primary analysis.

ITT population or full analysis set included all participants who were randomized, with study medication, regardless of whether participants received study medication or received a different drug from that to which they were randomized.

OS was defined as the time from date of randomization to date of death due to any cause. Participants without survival data beyond the date of their last follow-up were censored on the last date they were known to be alive. Data for this outcome measure was reported at final analysis.

ITT population or full analysis set included all participants who were randomized, with study medication, regardless of whether participants received study medication or received a different drug from that to which they were randomized.

One, two or three-year survival probability was defined as the probability of survival 1 year, 2 or 3 years after the date of randomization. The survival probability was estimated using the Kaplan-Meier method and 2-sided 95% confidence interval (CI) was calculated using the product limit method.

ITT population or full analysis set included all participants who were randomized, with study medication, regardless of whether participants received study medication or received a different drug from that to which they were randomized.

Laboratory abnormalities included anemia, hemoglobin increased, neutrophils (absolute), platelets, white blood cells, alanine aminotransferase (ALT), alkaline phosphatase, aspartate aminotransferase (AST), bilirubin (total), creatinine, hypercalcemia, hyperkalemia, hypermagnesemia, hypernatremia, hypoalbuminemia, hypocalcemia, hypokalemia, hypomagnesemia and hyponatremia. Laboratory abnormalities were graded by CTCAE version (v) 4.0 as Grade 1 = mild, Grade 2 = moderate, Grade 3 = severe and Grade 4 = life-threatening. Categories with at least 1 non-zero data values are reported.

AT population included all participants who received at least 1 dose of study medication, with treatment assignments designated according to actual study treatment received. Here, "Overall Number of Participants Analyzed" signifies participants evaluable for this outcome measure.