The study is being conducted to evaluate the clinical efficacy of HLX22 in combination with HLX87 as first-line treatment in patients with HER2-positive recurrent or metastatic breast cancer

The study consists of two stages Stage I is an open-label, multicenter, randomized, parallel-controlled phase II clinical study, and its primary objective is to evaluate the clinical efficacy of HLX22 in combination with HLX87 as first-line treatment in patients with HER2-positive recurrent or metastatic breast cancer based on ORR and PFS results.

Stage II is an open-label, multicenter, randomized, parallel-controlled phase III clinical study, and its primary objective is to evaluate the clinical efficacy of HLX22 in combination with HLX87 as first-line treatment in patients with HER2-positive recurrent or metastatic breast cancer based on PFS results.

Inclusion Criteria:

• 1. Have a full understanding of the study content, and sign the informed consent form (ICF); 2. Aged ≥ 18 years at the time of signing the ICF, male or female; 3. Histopathologically confirmed breast cancer that meets the following criteria:

  1. Advanced or metastatic breast cancer.
  2. HER2-positive as determined by the central laboratory, defined as IHC 3+, or IHC 2+ and ISH+.
  3. Positive or negative for hormone receptor HR (including estrogen receptor [ER] and progesterone receptor [PgR]) as determined by the central laboratory 4. No prior chemotherapy or HER2-targeted therapy for advanced or metastatic breast cancer (1 line of endocrine therapy is allowed).

  5. At least one measurable lesion as assessed by central imaging according to RECIST v1.1.

  7. Eastern Cooperative Oncology Group performance status score within 7 days prior to the first dose of study drugs: 0-1.

  8. Life expectancy ≥ 12 weeks. 9. Adequate organ functions

Exclusion Criteria:

• 1. History of a second malignancy within 3 years prior to signing the ICF. 2. Previous use of doxorubicin with a concentration of > 360 mg/m2 (or equivalent).

  3. Prior treatment with ADCs including exatecan derivatives that contain topoisomerase I inhibitors.

  4. Uncontrolled or significant cardiovascular diseases 5. Cerebrovascular accidents within 6 months prior to the first dose of study drugs.

  6. ILD/pneumonitis, or suspected ILD/pneumonitis or clinically significant lung-specific intercurrent illness .

  7. Active infection . 8. Presence of spinal cord compression or clinically symptomatic central nervous system metastases.

  9. Residual toxicity from previous anti-tumor therapy that has not resolved to Grade ≤ 1 as per NCI-CTCAE V6.0 or baseline level (except for alopecia).

  10. Presence of active tuberculosis. 11. Have received treatment with live attenuated vaccines within 30 days prior to the first dose of study drugs.

  12. Known history of severe allergic reaction to macromolecular protein preparations, hypersensitivity to the ingredient of the investigational products, or severe hypersensitivity to any excipient of the study drugs.

  13. Known history of abuse of psychotropic drugs or drug addiction. 14. Pregnant or lactating women.