An Open-Label, Randomized Phase III Study of Trastuzumab Rezetecan With or Without Everolimus in First to Third Line LAR Subtype TNBC

Inclusion Criteria: * Inclusion Criteria: 1. Female patients aged ≥18 years and ≤70 years; 2. Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1; 3. Life expectancy of at least 3 months; 4. Histologically confirmed invasive triple-negative breast cancer (defined as breast cancer with estrogen receptor \[ER\], progesterone receptor \[PR\], and human epidermal growth factor receptor 2 \[HER-2\] all determined to be negative by pathological testing. Specifically: ER-negative: IHC \<1%; PR-negative: IHC \<1%; HER2-negative: IHC -/+ or IHC ++ with FISH/CISH negative. All specimens must be verified as the LAR subtype of the Fudan quadruple molecular classification by the Precision Medicine Center/Department of Pathology at the study's participating center); 5. Tumor stage: recurrent or metastatic breast cancer; for locally recurrent disease, radical surgical resection must be confirmed by the investigator to be not feasible. Number of prior lines of therapy in the advanced setting ≤2; 6. Patients must have at least one lesion (measurable and/or non-measurable) that has not been previously irradiated, can be accurately assessed at baseline by CT/MRI, and can be repeatedly evaluated according to RECIST 1.1; 7. Adequate major organ function, meeting the following criteria: Hematological parameters: hemoglobin (HB) ≥90 g/L (without blood transfusion within 14 days); absolute neutrophil count (ANC) ≥1.5×10⁹/L; platelet count (PLT) ≥75×10⁹/L;Biochemical parameters: total bilirubin (TBIL) ≤1.5× upper limit of normal (ULN); alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤3×ULN; in the presence of liver metastases, ALT and AST ≤5×ULN; serum creatinine (Cr) ≤1×ULN, and calculated creatinine clearance \>50 mL/min (Cockcroft-Gault formula); 8. No prior radiotherapy, endocrine therapy, molecular targeted therapy, or surgery within 3 weeks before study initiation, and recovery from acute toxicities of prior treatment (if surgery was performed, the wound must be completely healed); no peripheral neuropathy or only grade I peripheral neurotoxicity; 9. Female subjects of childbearing potential must agree to use a medically accepted contraceptive method during the study treatment period and for at least 3 months after the last dose of study drug; 10. Subjects must voluntarily participate in this study, sign the informed consent form, have good compliance, and be willing to cooperate with follow-up. Exclusion Criteria: * Patients with any of the following criteria will be excluded from this study: 1. Known central nervous system (CNS) metastases or a history of CNS metastases prior to screening. For patients with clinically suspected CNS metastases, contrast-enhanced CT or contrast-enhanced magnetic resonance imaging (MRI) must be performed within 28 days before the first dose to rule out CNS metastases; 2. History of clinically significant or uncontrolled cardiac disease, including congestive heart failure, angina pectoris, myocardial infarction within the past 6 months, or ventricular arrhythmias; 3. Persistent adverse events of Grade ≥1 resulting from prior treatment. Exceptions to this are alopecia or conditions that the investigator deems should not preclude enrollment. Such cases should be clearly documented in the investigator's notes; 4. Major surgery (excluding minor procedures such as placement of vascular access) within 3 weeks before the first cycle of study treatment; 5. Pregnant or lactating patients; 6. Other malignancies within the past 5 years, excluding cured cervical carcinoma in situ, basal cell carcinoma of the skin, or squamous cell carcinoma of the skin; 7. Presence of third-space fluid accumulation (e.g., massive pleural effusion or ascites) that cannot be controlled by drainage or other methods; 8. Participation in another anti-tumor drug clinical trial within 3 weeks before the first use of the study drug; 9. Long-term unhealed wounds or incompletely healed fractures; 10. Active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection, or HBV DNA ≥500 IU/mL, or chronic hepatitis with abnormal liver function; 11. History of allergic constitution, known allergy to any component of the study drug regimen, or history of allergy to other monoclonal antibodies; 12. History of gastrointestinal bleeding within the past 6 months, or clear evidence of a tendency for gastrointestinal bleeding, such as esophageal varices at risk of bleeding, active local ulcerative lesions, or fecal occult blood test ≥ (++). Patients with fecal occult blood test (+) should undergo gastroscopy; 13. Abdominal fistula, gastrointestinal perforation, or intra-abdominal abscess within 28 days prior to study enrollment; 14. Urinalysis showing urine protein ≥ (++), or confirmed 24-hour urine protein quantification \>1.0 g; 15. Hypertension that cannot be controlled to within normal range with antihypertensive medication (systolic blood pressure \>140 mmHg, diastolic blood pressure \>90 mmHg); 16. Prior use of anti-angiogenic agents or prior exposure to an antibody-drug conjugate (ADC) with a topoisomerase I inhibitor as the payload