The study is being conducted to evaluate the pharmacokinetics and safety of SHR-A1811 monotherapy and in combination with Ritonavir or Itraconazole in subjects with HER2-expressing advanced breast cancer.

Inclusion Criteria:

1. ECOG score of 0 or 1;

2. Expected survival of not less than 3 months;

3. Important organ functions meet the following criteria:

   • Absolute neutrophil count (ANC) ≥1.5×109/L (1,500/mm3);
   • Platelet count (PLT) ≥100×109/L (100,000/mm3);
   • Hemoglobin (Hgb) ≥9.0 g/dL (90g/L);
   • Albumin level ≥3.0 g/dL;
   • Total serum bilirubin ≤1.5× the upper limit of normal (ULN);
   • Prothrombin time and activated partial thromboplastin time (aPTT) ≤1.5×ULN;
   • Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5×ULN (for patients with liver metastasis, ALT and AST ≤5×ULN);
   • Serum creatinine ≤1.5×ULN or creatinine clearance ≥60 mL/min;
   • QTcF ≤470 msec;
   • Left ventricular ejection fraction (LVEF) ≥50%.

Exclusion Criteria:

1. Known active central nervous system metastases that have not been treated with surgery or radiation, except those that have been stable for at least 1 month after treatment and have discontinued corticosteroids for >2 weeks;
2. Having cardiac diseases, such as severe/unstable angina, symptomatic congestive heart failure (NYHA II-IV), clinically significant supraventricular or ventricular arrhythmias requiring treatment or intervention, myocardial infarction within 6 months before the first administration, etc.
3. Known severe allergic history to any component of the SHR-A1811 product (ADC, total antibody, unconjugated toxin SHR169265 or its excipients), or hypersensitivity to humanized monoclonal antibody products (such as trastuzumab, pertuzumab, etc.);
4. Having contraindications to ritonavir or itraconazole use;
5. Having one or more factors that affect oral medication (such as inability to swallow, chronic diarrhea and intestinal obstruction, partial or total gastrectomy, etc.), or having active gastrointestinal diseases or other diseases that may significantly affect drug absorption, distribution, metabolism, or excretion.