Rationale: Around 70 to 80% of breast cancers are so-called "hormone-dependent" (HR+)/HER2-. For more than 50 years, studies have shown that chemotherapy and optimised hormonal treatments (hormone therapy), including a drug associated with ovarian suppression (OFS), improve survival in patients with these cancers, which are characterised by a high risk of relapse. However, younger patients suffer more side effects than older women, particularly from chemotherapy. This can affect their quality of life and reduce their ability to work. For post-menopausal women, genetic tests exist to assess whether chemotherapy is really necessary in addition to hormonal treatment. However, for high-risk premenopausal patients, chemotherapy is still systematically recommended, as no study has proved that it can be safely avoided. Clinical trials based on risk stratification using genetic tests have not been conclusive, but the majority of premenopausal women included had not received optimal hormone treatment. It is possible that the beneficial effect of chemotherapy is partly due to the artificial menopause it induces. Some experts believe that, for patients with a high clinical risk but a low genetic risk, an optimised hormonal treatment (drug + OFS) could suffice, without the need for chemotherapy. Objectives: Main objective: The aim of the study is to determine whether the use of a genetic test (Prosigna®) to decide whether or not to administer chemotherapy produces results as good as standard treatment (systematic chemotherapy) in premenopausal women with hormone-dependent (HR+) breast cancer/HER2-, by assessing their risk of cancer recurrence. The secondary objectives include verifying whether, in patients with a low Prosigna® score (around 70% of cases), optimised hormonal treatment (including suppression of ovarian function) is as effective as chemotherapy combined with hormonal in treatment preventing cancer recurrence. The study also seeks to compare the efficacy of treatment Prosigna®-guided versus systematic chemotherapy in terms of recurrence and quality of life, as well as economic aspects. Finally, the aim is to understand patients' concerns about the concept of reducing treatment (therapeutic de-escalation) and the way in which this information is communicated to them. The primary endpoint of the study is to measure the time elapsed between the start of participation in the study and the appearance of an event indicating a return of the cancer. This includes the return of cancer in the same breast or neighbouring areas, the spread of cancer to other parts of the body, the appearance of new cancer in the other breast or death from any cause. Trial Population: The study includes women major premenopausal diagnosed with invasive, hormone receptor-positive (ER+) and HER2-negative breast cancer. Patients must have undergone breast and axillary surgery recent and have a tumour sample suitable for analysis by the testProsigna® . They must be able to receive the study treatments Postmenopausal women, women with stage IV breast cancer, women who have already received adjuvant systemic treatment (except short neoadjuvant hormone therapy), women with a recent history of invasive cancer, pregnant women or women who are breast-feeding will not be able to take part in the study. Interventions: After agreeing to take part, patients will enter the pre-inclusion period (up to 28 days before randomisation), during which the investigator will carry out all the necessary tests to assess their eligibility. The investigator will then randomise the patients to find out which treatment they have been assigned, no more than 2 weeks later: the experimental group will receive a treatment decided on the basis of the results of a genomic test: either chemotherapy and hormone therapy, or hormone therapy alone. The control group will receive the standard treatment. The treatment and follow-up phases are the same as for standard care. Information on the quality of life patient's will and other information (associated costs, perception of their participation in the study, etc.) also be collected by means of questionnaires completed by the patients during the 5 years following randomisation.
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invasive breast cancer free survival (IBCFS)
Timeframe: Time from the date of randomization to the date of the first event (ipsilateral loco-regional invasive breast or distant breast cancer recurrence, contralateral new invasive primary breast cancer or death from any cause), assessed up to 120 months