The primary objective is to assess the 5-year distant recurrence-free interval (dRFI, according to STEEP criteria version 2.0) [9] in all patients treated by (intensified) endocrine therapy alone (and with ovarian suppression in cases with enhanced clinical risk according to current AGO-recommendations)

to assess 10-year dRFI, according to STEEP 2.0 criteria, in all patients treated by (intensified) endocrine therapy alone (and with ovarian suppression in cases with enhanced clinical risk according to current AGO-recommendations)  to assess 5- and 10-year dRFI, according to STEEP 2.0 criteria, in all patients treated by SOC chemotherapy treatment followed by ET+/-OFS  to assess 5- and 10-year distant disease-free survival (dDFS, according to STEEP 2.0) in all patients and all treatment groups (i.e., patients treated by ET alone, ET + GnRH, chemotherapy followed by ET, chemotherapy followed by ET + GnRH, OFS-treated patients)  to assess 5- and 10-year overall survival (OS) in all patients and all treatment groups  to assess 5- and 10-year breast cancer-free interval (BCFI, according to STEEP 2.0) in all patients and all treatment groups  to describe and compare the quality of life (QLQ BR23 and QLQ-C30) at baseline, 3 months, 6 months, 12 months, 18 months, 2 years, 3 years 4 years and after 5 years between all treatment groups  to capture adherence to OFS and endocrine treatment in all patients  to assess concordance between BluePrint®/MammaPrint® molecular subtyping results vs. pathological immune-histochemistry results  to assess endocrine response measured by post-endocrine Ki-67 (≤10% and/or relative change vs. baseline) in patients treated by preoperative ET according to MammaPrint® result  to perform sub analyses of all endpoints using the MINDACT clinical high-risk clientele definition (i.e., G1, N0, tumor size >3cm and N+, tumor size >2-5cm; G2, N0, tumor size >2cm and N+, any tumor size; G3, N0, tumor size >1cm and N+, any tumor size)  to assess the prognostic value of ultralow versus low MammaPrint® assessment for dRFI and OS  to assess the additional prognostic value of ultralow / low MammaPrint® assessment adjusted for clinicopathological markers (histology, grade, expression levels of ER, PR, HER2 and Ki-67 at baseline and after preoperative endocrine therapy) for dRFI and OS  5 and 10-year iDFS in node-negative patients with ultralow MammaPrint® treated by shorter duration of ET (2-3 years at investigator decision) Endpoints Primary endpoint: 5-year distant recurrence-free interval (dRFI, according to STEEP criteria version 2.0) [9] in all patients treated by (intensified) endocrine therapy alone (and with ovarian suppression in cases with enhanced clinical risk according to current AGO-recommendations).

Prä- und perimenopausale Patientinnen mit luminalem Brustkrebs/Mammakarzinom im Frühstadium mit mittlerem bis hohem klinischen Rezidivrisiko und geringem genomischen Rezidivrisiko

Female breast cancer patients  Pre- or perimenopausal at registry entry (age <60 years and state after hysterectomy or amenorrhea for <12 months: confirmation by blood hormone levels (FSH and estradiol in premenopausal range as per local normal range) recommended)  Primary tumor diagnosis not older than three months prior to inclusion (primary diagnosis defined as date of initial tumor biopsy)  Estrogen- and/or progesterone-receptor-positive/HER2 negative early breast cancer without any clinical signs of metastases Adequate risk for recurrence:  intermediate clinical risk for recurrence, defined as (clinical in case of neoadjuvant treatment):  c/pT1 and  c/pN0 and  Ki-67 15-24% or  G2 or patients, who do not meet these criteria but are at intermediate clinical risk for recurrence at investigator decision (e.g., very young age, low expression of hormone receptors etc.) can be included on individual decision basis or  high clinical risk for recurrence, defined as either (clinical in case of neoadjuvant treatment):  c/pT2-4 or  c/pN1 or  Ki-67 ≥25% or  G3  Low genomic risk of recurrence by MammaPrint® (tested on treatment naïve tumor specimen)  Luminal-type by BluePrint®  Treatment according to standard-of-care (e.g., AGO Guidelines) planned or started (until completion of local therapy the latest, including started or completed endocrine induction therapy, started, or planned adjuvant or neoadjuvant treatment)  Availability of untreated tumor material (core biopsy if preoperative endocrine therapy performed or neoadjuvant treatment intended or surgery specimen)  Capability to give written informed consent  Nodal positive patients will be accepted to the registry up to 25% of the genomic low/ultralow-risk population (n=441).

Any other genomic testing, besides MammaPrint®/BluePrint®, has been performed on the tumor material  Medical or psychological conditions that would not permit the patient to sign informed consent  Legal incapacity or limited legal capacity  Current participation in any interventional clinical trial with medicinal products  Non-compliance of the patient