Decreasing Treatment for Metastatic HER2-Positive Breast Cancer With Undectable Cancer Levels in Blood Tests.

Inclusion Criteria

• •1. Patient must have signed a written informed consent prior to any trial specific procedures. When the patient is physically unable to give their written consent, a trusted person of their choice, independent from the investigator or the sponsor, can confirm in signing the patient's consent;
• •2. Men or women ≥18 years of age;
• •3. Documented diagnosis of locally advanced inoperable or metastatic histologically-proven HER2-positive breast cancer (HER2-positive is defined as HER2 3+ immunohistochemical overexpression, or the presence of HER2 amplification, according to ASCO-CAP guidelines);
• •4. Must have an adequate archival tumor tissue sample available for next-generation sequencing (NGS) analysis by central laboratory, in order to design the ctDNA test (based on most recent available tumor tissue sample, metastatic biopsy (bone tissue excluded) and primary tumor authorised);
• •5. Patient with Eastern Cooperative Oncology Group - Performance Status (ECOG-PS) ≤1;
• •6. Patient must have received continuous anti-HER2 targeted therapy (including Trastuzumab, Trastuzumab/Pertuzumab, Trastuzumab-Deruxtecan or T-DM1) treatment for at least 2 years in any line setting, for their locally advanced inoperable or metastatic HER2 + breast cancer (prior treatment interruption of 3 months maximum is allowed), with complete response or partial response at last radiological assessment;
• •Note: the number of patients who received anti-HER2 targeted therapy in second line setting or more will be capped to 50% of the overall population
• •7. In case of bone disease only, complete metabolic response in 18-FDG pet-scanner is required;
• •8. Patient with treated (surgery and/or radiation therapy) and controlled primary tumor;
• •9. Patients with ER-positive disease may or may not have received concomitant endocrine therapy (which must be continued if present). Concomitant ovarian blockade using Luteinizing Hormone-Releasing Hormone (LHRH) agonists is authorised as well;
• •10. Adequate cardiac, renal, haematological and hepatic functions according to guidelines hospital;
• •11. Women of childbearing potential must have a negative serum or urine pregnancy test done within 28 days before inclusion;
• •12. Non post-menopausal women and fertile men must agree to use adequate contraception methods during the study. Hormonal contraceptives such as birth control pills, patches, implants, or injections are not allowed in patients who are hormone receptor positive;
• •13. Patients must be willing and able to comply with the protocol for the duration of the study including scheduled visits, treatment plan and other study procedures including follow-up;
• •14. Patients must be affiliated to a Social Security System (or equivalent).