Inclusion Criteria:
1. Aged 18-75 years, female;
2. Histologically confirmed invasive breast cancer with lung metastasis (diagnosed via contrast-enhanced chest CT, PET-CT, or MRI);
3. Disease progression after at least 1 line of systemic therapy containing chemotherapy for recurrent/metastatic disease (per RECIST 1.1 criteria);
4. At least one measurable lung metastatic lesion (≥10 mm on spiral CT/MRI, not previously treated with radiotherapy) per RECIST 1.1;
5. Adequate organ function (e.g., hemoglobin ≥90 g/L, alanine transaminase/aspartate transaminase ≤3× upper limit of normal \[ULN\], serum creatinine ≤1× ULN, no severe arrhythmia or myocardial ischemia on ECG);
6. ECOG performance status ≤2 and life expectancy ≥3 months;
7. Use of medically approved contraception (for women of childbearing potential) during treatment and for at least 3 months after the last treatment;
8. Voluntary participation, signed informed consent, and willingness to comply with treatment and follow-up.
Exclusion Criteria:
1. Received radiotherapy (excluding palliative radiotherapy) within 3 weeks prior to treatment; received major surgery (excluding minor outpatient procedures such as vascular access placement) within 3 weeks before the first cycle of study treatment;
2. Persistent grade ≥2 adverse events from prior treatments (e.g., chemotherapy, surgery) (except alopecia or conditions the investigator deems should not result in exclusion);
3. History of clinically significant or uncontrolled cardiac disease, including congestive heart failure, angina pectoris, myocardial infarction within the past 6 months, or ventricular arrhythmias;
4. Presence of third-space fluid accumulation that cannot be controlled by drainage or other methods;
5. Active HBV or HCV infection (HBV DNA ≥500 IU/ml or positive HCV RNA) with abnormal liver function;
6. Currently pregnant or breastfeeding;
7. Allergic diathesis, or known history of allergy to components of the conventional treatment medications in this study, or to HBOT-related equipment/gas components (e.g., pure oxygen);
8. Presence of contraindications to HBOT, such as untreated pneumothorax, pulmonary bullae, severe emphysema, history of epilepsy (with seizures within the past 2 years), or acute exacerbation of severe sinusitis/otitis media.
