Previous studies have shown differences in the effects of different endocrine drugs on blood lipids in breast cancer, and dyslipidaemia is a major risk factor for cardiovascular disease, and it has been previously reported that the leading cause of death in postmenopausal patients with breast cancer is cardiovascular disease, but the effects of endocrine drug therapy on blood lipids in young breast cancer patients (age ≤40) are not clear. Previously, our group conducted a preliminary retrospective analysis of young patients on endocrine therapy and found that dyslipidaemia was also a common adverse effect of treatment in young breast cancer patients; therefore, dyslipidaemia induced by antineoplastic therapy not only occurs in postmenopausal patients, but is also prevalent in premenopausal and even younger patients. Therefore, this study intends to evaluate the effects of different treatment regimens on lipids in early-stage young breast cancer patients and to explore the optimal timing of lipid-lowering drug interventions to provide a basis for clinical practice.

Inclusion Criteria:

• ECOG score 0-1
• Resectable breast cancer
• No distant metastases on postoperative imaging assessment
• Patients proposed for (neo)adjuvant therapy
• No previous oral lipid-lowering drugs, serum LDL-C level within normal range, i.e. LDL-C value: <3.4 mmol/L
• No fatty liver by liver ultrasound/CT examination
• No major organ dysfunction

Exclusion Criteria:

• Patients with pre-existing hyperlipidaemia, coronary heart disease, fatty liver disease, or who have received or are receiving lipid-lowering medication
• Enrolled in another study or less than or equal to 4 weeks since discontinuation of other medications
• Presence of severe dysfunction of vital organs
• Patients with other malignancies (except cured non-melanoma skin cancer, cervical carcinoma in situ and other tumours that have been cured for at least 5 years)
• Acute infectious diseases or chronic infectious diseases in active stage
• History of uncontrolled epilepsy, central nervous system disease or mental disorder

Young breast cancer patients who fulfil the following criteria: less than or equal to 40, surgically resectable, requiring (neo)adjuvant chemotherapy or endocrine therapy.