This study is a single-center, prospective/retrospective, observational clinical research designed to compare the differences in peripheral blood components between young and elderly HR+HER2- breast cancer patients, and to identify peripheral blood components that may affect the prognosis of young HR+HER2- breast cancer patients.

The study population consists of early-stage HR+HER2- breast cancer patients receiving neoadjuvant therapy. Eligible patients who require neoadjuvant treatment will be enrolled in the study. Retrospective data and samples will be collected based on existing patient medical records and tissue biobank samples. Prospective data collection will be based on routine clinical treatment during the study period and will continue until the patient completes neoadjuvant therapy and undergoes primary tumor surgery, or until the study is prematurely terminated.

HR+HER2- breast cancer patients receiving neoadjuvant therapy will be divided into young and elderly groups. Peripheral blood samples will be collected at baseline (T0, prior to treatment) and after two cycles of neoadjuvant therapy (T1). Paired baseline tumor biopsy samples and/or surgical tumor samples will also be collected. Peripheral blood and tumor samples will undergo appropriate tests.

The study respects the investigator's choice of treatment, without specifying which drugs should be used, the dosage, the administration mode (including monotherapy, combination therapy, or sequential therapy), or the duration of treatment.

Inclusion Criteria:

1. Signed informed consent according to local regulations;
2. Age ≥ 18 years;
3. Female;
4. Histologically/cytologically confirmed breast cancer;
5. Determined by immunohistochemistry to be ER+ or PR+ (with at least 1% of cells expressing estrogen receptors) and HER2-.

Exclusion Criteria:

1. Presence of distant metastasis;
2. History of other malignancies. Patients with basal cell carcinoma or squamous cell carcinoma of the skin, cervical carcinoma in situ, or other cancers who have been disease-free for more than 5 years after appropriate treatment may be included;
3. Participation in another clinical trial within 30 days prior to starting neoadjuvant treatment for breast cancer, and receiving investigational drugs or any concomitant treatment including investigational drugs;
4. Immunodeficiency or HIV infection;
5. Severe heart, lung, liver, or kidney dysfunction;
6. Uncontrolled infections or active infections;
7. Pregnant or breastfeeding women.

The study population consists of early-stage luminal breast cancer patients receiving neoadjuvant therapy.