abemaciclib in combination with an endocrine therapy ± LHRH as described in the current effective summary of product characteristics. This is an observational study. There is no treatment allocation. The decision to initiate treatment will be based solely on clinical judgement.

endocrine monotherapy ± LHRH. This is an observational study. There is no treatment allocation. The decision to initiate treatment will be based solely on clinical judgement.

Patients' individual perception of risk of recurrence and treatment decision assessed by questionnaire at baseline. The questionnaire is provided in two versions, with one version containing 6 items (applicable for the ET mono cohort), and the other version containing 11 items (applicable for ribociclib and abemaciclib cohorts). Responses are primarily given by selecting from predefined options, with some questions allowing multiple answers or prioritization. The scales and response options are designed to reflect individual preferences, concerns, and decision-making processes of patients. Higher scores on the importance scale indicate a stronger motivation to reduce recurrence risk

iDFS using STEEP criteria. iDFS is defined as the time from study start to the date of the first event of invasive ipsilateral breast tumor recurrence, local/regional invasive recurrence, distant recurrence, death (any cause), contralateral invasive BC, or second primary non-breast invasive cancer (excluding basal and squamous cell carcinomas of the skin).

iBCFS using STEEP criteria. iBCFS is defined as the time from study start to the date of the first event of invasive ipsilateral breast tumor recurrence, local/regional invasive recurrence, distant recurrence, death (any cause), or contralateral invasive BC.

RFS using STEEP criteria. RFS is defined as the time from study start to the date of the first event of invasive ipsilateral breast tumor recurrence, local/regional invasive recurrence, distant recurrence, or death (any cause).

DDFS using STEEP criteria. DDFS is defined as the time from study start to the date of the first event of distant recurrence, death (any cause), or second primary non-breast invasive cancer (excluding basal and squamous cell carcinomas of the skin).

Incidence and severity of adverse events

Proportion of patients with dose modification and underlying cause

Proportion of patients with treatment interruption and underlying cause

Proportion of patients who discontinued treatment and underlying cause

Time from treatment start to permanent treatment discontinuation

Changes from baseline as assessed by European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ)-C30. The EORTC QLQ-C30 is a participant completed 30 item questionnaire that is composed of both multi-item scales and single-item measures. These include five functional scales, three symptom scales, six single items and a GHS/QoL scale. All of the scales and single-item measures range in score from 0 to 100. A high scale score represents a higher response level.

Changes from baseline as assessed by European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ)-BR42. The Breast Cancer Module EORTC QLQ-BR42 is a 42 item instrument designed to measure quality of life in breast cancer participants. It includes three functional scales, six symptom scales and three single items. All the scales and single item measures range in score from 0 to 100. A high scale score represents a higher response level.

Changes from baseline as assessed by the Hospital Anxiety and Depression Scale (HADS D). The HADS is a participant completed fourteen item scale. Seven of the items relate to anxiety and seven relate to depression. The anxiety and depression subscales each range from 0 to 21, with higher scores indicating higher anxiety/depression complains.

Medication Adherence Report Scale (MARS-D) questionnaire is a 5-item questionnaire measuring non-adherence. Each item is ranging from "never" (5 points) to "always" (1 point), with a total score 5-25 where higher scores indicate better compliance.

Participant compliance as assessed by a physician adherence rated as very good, good, moderate, or poor.

Participant compliance as assessed by neutrophil count.

Medication Adherence Report Scale (MARS-D) questionnaire is a 5-item questionnaire measuring non-adherence. Each item is ranging from "never" (5 points) to "always" (1 point), with a total score 5-25 where higher scores indicate better compliance.

Medication Adherence Report Scale (MARS-D) questionnaire is a 5-item questionnaire measuring non-adherence. Each item is ranging from "never" (5 points) to "always" (1 point), with a total score 5-25 where higher scores indicate better compliance.

The Work Productivity and Activity Impairment - General Health questionnaire (WPAI-GH) is a participant completed 6 item questionnaire which addresses absenteeism, presenteeism, overall work productivity loss, and activity impairment for the 7 days prior to the assessment. WPAI outcomes are presented as impairment percentages (range goes from 0 to 100 with a higher percentage indicating greater impairment and less productivity).

Reported reasons for treatment discontinuation

Type of subsequent anti-neoplastic therapies will be recorded

Time from study start to first subsequent anti-neoplastic therapy

Participant compliance assessed by MARS-D and active participation of the participant in the treatment decision assessed by the questionnaire "Fragebogen zur partizipativen Entscheidungsfindung aus Participantensicht" (PEF-FB-9) and "Fragebogen zur partizipativen Entscheidungsfindung aus Sicht des Arztes"(PEF-FB-Doc) at baseline.

The MARS-D is a 5-item questionnaire measuring non-adherence with a total score of 5-25 where higher scores indicate better compliance.

The PEF-FB-9 is a participant completed 9 item questionnaire for participant participation in decision-making. The 9 items are rated on a 6-point scale with endpoints ranging from "does not apply at all" to "applies completely", summed up and transformed into a scale from 0 to 100. The higher the total score, the higher the perceived degree of participation.

The PEF-FB-Doc is the physician version of the PEF-FB-9.

The correlation between participation on treatment decisions and participant compliance will be presented.

Participant compliance assessed by MARS-D and participants' fear of cancer recurrence assessed by the Fear of Cancer Recurrence (FCR)-1 questionnaire.

The MARS-D questionnaire is a 5-item questionnaire measuring non-adherence. Each item is ranging from "never" (5 points) to "always" (1 point), with a total score 5-25 where higher scores indicate better compliance.

The FCR-1 is a participant completed 1 item questionnaire asking the participant to describe their subjective level of fear of cancer recurrence at the given time on a scale from 0 to 100 with 100 being the greatest fear.

The correlation between participants' fear of recurrence and participant compliance will be presented.

Treatment expectation assessed by a questionnaire containing 5 questions with each 5-7 ordinal answer categories with the same directionality on participants' expectations regarding therapy, side effects and management

Treatment satisfaction assessed by a questionnaire containing 5 questions with each 5-7 ordinal answer categories with the same directionality on treatment satisfaction