PFS time was measured from the date of randomization to the date of investigator-determined objective progression as defined by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, or death from any cause. Progressive Disease (PD) was at least a 20% increase in the sum of the diameters of target lesions, with reference being the smallest sum on study and an absolute increase of at least 5 mm, or unequivocal progression of non-target lesions, or 1 or more new lesions. If a participant does not have a complete baseline disease assessment, then the PFS time was censored at the date of first dose, regardless of whether or not objectively determined disease progression or death has been observed for the participant. If a participant was not known to have died or have objective progression as of the data inclusion cutoff date for the analysis, the PFS time was censored at the last adequate tumor assessment date.

All enrolled participants. Censored participants: Abemaciclib + Trastuzumab + Fulvestrant=23; Abemaciclib + Trastuzumab = 18 and Trastuzumab + Standard of Care Chemotherapy = 27.

OS is defined as the time from the date of randomization until death from any cause. For participants not known to have died by the data-inclusion cutoff date, OS is censored at the last date they were known to be alive. For each treatment arm OS rate at 1 year from the date of randomization was determined using the OS times and was estimated using the Kaplan-Meier method.

All randomized participants (including the censored participants). Number of participants censored were "150 mg Abemaciclib + 8 mg/kg Trastuzumab + 500 mg Fulvestrant = 62," "150 mg Abemaciclib + 8 mg/kg Trastuzumab = 62," and "8 mg/kg Trastuzumab + Standard of Care Chemotherapy = 58."

OS is defined as the time from the date of randomization until death from any cause. For participants not known to have died by the data-inclusion cutoff date, OS is censored at the last date they were known to be alive. For each treatment arm OS rate at 2 years from the date of randomization was determined using the OS times and was estimated using the Kaplan-Meier method.

All randomized participants (including the censored participants). Number of participants censored were "150 mg Abemaciclib + 8 mg/kg Trastuzumab + 500 mg Fulvestrant = 47," "150 mg Abemaciclib + 8 mg/kg Trastuzumab = 47," and "8 mg/kg Trastuzumab + Standard of Care Chemotherapy = 41."

OS is defined as the time from the date of randomization until death from any cause. For participants not known to have died by the data-inclusion cutoff date, OS is censored at the last date they were known to be alive. For each treatment arm OS rate at 3 years from the date of randomization was determined using the OS times and was estimated using the Kaplan-Meier method.

All randomized participants (including the censored participants). Number of participants censored were "150 mg Abemaciclib + 8 mg/kg Trastuzumab + 500 mg Fulvestrant = 41," "150 mg Abemaciclib + 8 mg/kg Trastuzumab = 37," and "8 mg/kg Trastuzumab + Standard of Care Chemotherapy = 33."

ORR was the percentage of participants achieving a best overall response (BOR) of complete response (CR) or partial response (PR) as per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. CR defined as the disappearance of all target and non-target lesions and no appearance of new lesions. PR defined as at least a 30% decrease in the sum of the longest diameters (LD) of target lesions (taking as reference the baseline sum LD), no progression of non-target lesions, and no appearance of new lesions.

All enrolled participants.

DoR was the time from the date of first evidence of complete response or partial response to the date of objective progression or the date of death due to any cause, whichever is earlier. CR and PR were defined using the RECIST v1.1. CR defined as the disappearance of all target and non-target lesions and no appearance of new lesions. PR defined as at least a 30% decrease in the sum of the LD of target lesions (taking as reference the baseline sum LD), no progression of non-target lesions, and no appearance of new lesions. If a responder was not known to have died or have objective progression as of the data inclusion cutoff date, duration of response was censored at the last adequate tumor assessment date.

All enrolled participants who received at least one dose of study drug and achieved CR or PR.Censored participants = 12 in 150 mg Abemaciclib + 8 mg/kg Trastuzumab + 500 mg Fulvestrant

; 3 participants in 150 mg Abemaciclib + 8 mg/kg Trastuzumab and 11 participants in 8 mg/kg Trastuzumab + Standard of Care Chemotherapy.

Disease Control Rate (DCR) was the percentage of participants with a best overall response of CR, PR, or Stable Disease (SD) as per Response using RECIST v1.1 criteria. CR defined as the disappearance of all target and non-target lesions and no appearance of new lesions. PR defined as at least a 30% decrease in the sum of the LD of target lesions (taking as reference the baseline sum LD), no progression of non-target lesions, and no appearance of new lesions. SD was neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD for target lesions, no progression of non-target lesions, and no appearance of new lesions.

All enrolled participants.

Clinical benefit rate defined as percentage of participants with best overall response of CR, PR, or SD with a duration of at least 6 months. CR, PR, or SD were defined using RECIST, v1.1 criteria. CR defined as the disappearance of all target and non-target lesions and no appearance of new lesions. PR defined as at least a 30% decrease in the sum of the LD of target lesions (taking as reference the baseline sum LD), no progression of non-target lesions, and no appearance of new lesions. SD was neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD for target lesions, no progression of non-target lesions, and no appearance of new lesions. Percentage of participants = (participants with CR+PR+SD with a duration of at least 6 months /number of participants enrolled) *100.

All enrolled participants.

The mBPI-sf is an 11-item instrument used as a multiple-item measure of cancer pain intensity. In addition to pain intensity (4 items), the mBPI-sf is designed for participants to record the presence of pain in general, pain relief, and pain interference with function (general activity, mood, ability to walk, ability to perform normal work, relations with others, sleep, enjoyment of life). Responses for the mBPI-sf items are captured through the use of 11-point numeric rating scales anchored at 0 (no pain or does not interfere) and 10 (pain as bad as you can imagine or completely interferes). The mBPI-sf recall period is 24 hours and typical completion time for this instrument is less than 5 minutes. Mean Interference Score data is reported here. Least square (LS) Mean value was controlled for Treatment, visit, Treatment*Visit and baseline.

All enrolled participants.

EORTC QLQ-C30 v3.0 was a self-administered questionnaire with multidimensional scales that measures 5 functional domains (physical, role, cognitive, emotional, and social), global health status, and symptom scales of fatigue, pain, nausea and vomiting, dyspnea, loss of appetite, insomnia, constipation and diarrhea, and financial difficulties. A linear transformation is applied to standardize the raw scores to range between 0 and 100 per developer guidelines. For functional domains and global health status, higher scores represent a better level of functioning. For symptoms scales, higher scores represented a greater degree of symptoms. LS Mean value was controlled for Treatment, visit, Treatment*Visit and baseline.

All randomized participants who received at least one dose of study drug with baseline and post-baseline EORTC QLQ-C30 data for each EORTC QLQ-C30 items.

The EQ-5D-5L is a standardized instrument for use as a measure of self-reported health status. Participants completed the 5-level (no problem, slight problem, moderate problem, severe problem, and inability or extreme problem), 5-dimension (mobility, self-care, usual activities, pain/discomfort, and anxiety/depression) questionnaire concerning their current health state. Five dimensions of health status are each assessed with 5 response options and scored as a composite index which were anchored on a scale of 0 to 1 with a higher score representing better health status.LS Mean value was controlled for Treatment, visit, Treatment*Visit and baseline.

All enrolled participants who received at least one dose of study drug with baseline and post-baseline EQ-5D 5L data.

European Quality of Life-5 Dimensions-5 Level (EQ-5D-5L) is a standardized measure of health status of the participant. The EQ-5D-5L is assessed using a visual analog scale (VAS) that ranged from 0 to 100 millimeter (mm), where 0 is the worst health you can imagine and 100 is the best health you can imagine. A higher score indicates better health state. LS Mean value was controlled for Treatment, visit, Treatment*Visit and baseline.

All enrolled participants who received at least one dose of study drug with baseline and post-baseline EQ-5D 5L VAS data.

Minimum Steady State Concentration (Cmin,ss) of Abemaciclib and Its Metabolites (M2 and M20) was evaluated. M2 and M20 are 2 major active metabolites of abemaciclib.

All enrolled participants who received at least one dose of study drug and had evaluable PK data.