Reduction of treatment after Complete Response in Advanced Hormone-Sensitive Breast Cancer

Prior treatment

• Prior chemotherapy for advanced or metastatic disease.
• Major surgery within 2 weeks prior to enrolment.
• Current participation in another interventional clinical trial evaluating an investigational product, or receipt of an investigational agent within 28 days prior to enrolment and during the study period.

Other illness

• Disease progression under CDK4/6 inhibitor.
• History of malignancy other than the breast cancer under study, except for adequately treated basal cell or squamous cell carcinoma of the skin, or carcinoma in situ of the cervix, unless the patient has been disease-free and off treatment for at least 3 years.
• History of carcinomatous meningitis or central nervous system metastases.
• Any medical condition that could interfere with study procedures or patient compliance.

Other

• Detectable tumor-derived ctDNA at screening, as assessed by the Signatera™ Genome test.
• Patients under legal guardianship, deprived of liberty by judicial or administrative decision, or unable to provide informed consent.
• Patients unwilling or unable to comply with required medical follow-up due to geographic, social, or psychological reasons.
• Pregnant or breastfeeding women, or participants unwilling to use highly effective contraception as defined in the protocol.

• The patient must have provided written informed consent prior to any study-specific procedures. When the patient is physically unable to provide written consent, an impartial witness, independent from the investigator and the sponsor, may confirm consent by signing on the patient’s behalf.
• The patient must be affiliated with a social security system.
• The patient must be willing and able to comply with the study protocol, including treatment administration, scheduled visits, examinations, and follow-up.
• Female or male patients aged 18 years or older.
• Documented diagnosis of adenocarcinoma of the breast with evidence of locoregional recurrent or metastatic disease, who are not eligible for local treatment in case of locoregional recurrent disease, that meets the following criteria by local testing: - Hormone receptor-positive, defined by estrogen receptor (ER) expression or progesterone receptor (PR) expression in at least 10% of tumor cells of tumor cells by immunohistochemistry
• Participants must have documentation of HER2-negative tumour according to the American Society of Clinical Oncology (ASCO) and College of American Pathologists (CAP) guidelines and based on the most recent available results. HER2-negative status is defined as an immunohistochemical (IHC) score of 0 or 1+, or an IHC score of 2+ with negative in situ hybridization (ISH) (HER2/CEP17 ratio <2 or, for single-probe assessment, HER2 copy number <4).
• Complete response, or partial response with sclerotic bone-only disease, maintained for at least 6 months, according to RECIST version 1.1 criteria. (assessed on TAP CT or TEP TDM).
• Availability of an adequate archived tumor tissue sample for next-generation sequencing (NGS) analysis performed by Natera laboratory, allowing the design of a personalized ctDNA assay based on the most recent available tumor specimen.
• Patients on first-line metastatic treatment with a CDK4/6 inhibitor in combination with an aromatase inhibitor, with or without an LHRH agonist for at least 24 months.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Women of childbearing potential must have a negative serum pregnancy test within 28 days prior to initiation of study treatment; Women of childbearing potential must use a highly effective non-hormonal method of contraception throughout the study and for at least 3 weeks after taking the last dose of study treatment. Male participants who intend to be sexually active with a female partner of childbearing potential must be surgically sterile or using an acceptable method of contraception until at least 3 weeks after the last treatment administration (14 weeks if the patient is taking palbociclib).