A Study to Determine the Efficacy of a Digital Self-management Support Tool to Improve the Quality of Life During Adjuvant HOrmonal Therapy for Patients With Early Breast Cancer

Inclusion Criteria: 1. Documentation of Disease: 1. Subjects must have histologically confirmed ER and/or PgR positive HR+ invasive BC; 2. Subjects must have stage I to III breast cancer and no evidence of distant metastatic or locally recurrent disease; NB: Bilateral breast carcinoma is allowed; NB: Patients with personal history of previous breast cancer or Ductal Carcinoma in situ (DCIS) are eligible for the protocol; 2. Indication to receive adjuvant endocrine therapy (tamoxifen or aromatase inhibitors) with or without targeted agents (e.g., CDK 4/6 inhibitors, PARP inhibitors, bisphosphonates); 3. Prior treatment: Patients must be actively on ET for their breast cancer diagnosis (any type, including either tamoxifen or an aromatase-inhibitor with or without targeted agents) at the time of study enrollment; 4. Documentation of side effects of ongoing ET: Any endocrine therapy related adverse effects should be reported during treatment with endocrine therapy; 5. Others: 1. Age ≥ 18 years; 2. ECOG Performance Status 0,1 or 2; 3. Patients should possess a smartphone; 4. Patient should understand, sign, and date the written informed consent form prior to any protocol-specific procedures performed; 5. Patient should be able and willing to comply with study visits and procedures as per protocol; 6. Patients must be affiliated to a social security system or beneficiary of the same; 7. Able to readily read and understand French; NB: Patients may have breast reconstruction during protocol participation; NB: Biologic therapy, targeted therapy and bisphosphonates are acceptable during protocol participation; NB: Male patients can be included in the trial; NB: Pharmacological or other non-pharmacological interventions for endocrine treatment for adverse effects are accepted at physician discretion. Exclusion Criteria: 1. Severe cognitive impairments or severe psychiatric disorders (assessed by the investigator or mentioned in the medical file of the patient) which in the investigator's opinion would jeopardize compliance with the protocol; 2. Patient under guardianship or deprived of her/his liberty by a judicial or administrative decision or incapable of giving her/his consent; 3. Patients participating at enrollment in a behavioral interventional trial; 4. Patients suffering from physical related reversible and treatable causes of the entry endocrine therapy-related adverse events (e.g. but not limited to anemia, electrolytes unbalance, infections, renal dysfunction, active metastases hormonal unbalances \[hypothyroidism, adrenal insufficiency, etc.\] - according to physician's judgement.