Inclusion Criteria:
1. Voluntarily sign the informed consent form and agree to comply with the protocol requirements;
2. No gender restriction;
3. Age: ≥18 and ≤75 years (Phase Ia); ≥18 years (Phase Ib);
4. Expected survival ≥3 months;
5. Locally advanced or metastatic esophageal squamous cell carcinoma, gastric cancer, colorectal cancer, or other solid tumors;
6. Agree to provide archived tumor tissue specimens or fresh tissue samples from primary or metastatic lesions obtained within 2 years;
7. Must have at least one measurable lesion as defined by RECIST v1.1;
8. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1;
9. Toxicities from prior anti-tumor therapy must have recovered to ≤ Grade 1 as defined by NCI-CTCAE v6.0;
10. No severe cardiac dysfunction, with left ventricular ejection fraction (LVEF) ≥50%;
11. Organ function levels must meet the protocol-specified requirements;
12. Coagulation function: International Normalized Ratio (INR) ≤1.5, and activated partial thromboplastin time (aPTT) ≤1.5 × upper limit of normal (ULN);
13. Urine protein ≤2+ or ≤1000 mg/24h;
14. For premenopausal women of childbearing potential, a pregnancy test must be performed within 7 days prior to the start of treatment, with a negative serum pregnancy test result, and they must be non-lactating; all study participants (both male and female) must use adequate barrier contraception throughout the entire treatment period and for 7 months after the completion of treatment.
Exclusion Criteria:
1. Use of chemotherapy, biotherapy, immunotherapy, or other anti-tumor therapies within 4 weeks or 5 half-lives prior to the first dose;
2. History of severe cardiac disease;
3. QT interval prolongation, complete left bundle branch block, or third-degree atrioventricular block;
4. Active autoimmune diseases and inflammatory diseases;
5. Diagnosis of another malignant tumor within 5 years prior to the first dose;
6. Hypertension inadequately controlled by two antihypertensive agents;
7. History of interstitial lung disease (ILD) requiring corticosteroid therapy, or current ILD, or radiation pneumonitis of Grade ≥2;
8. Active central nervous system (CNS) metastases;
9. Subjects with a history of allergy to recombinant humanized antibodies or human-mouse chimeric antibodies, or allergy to any excipient component of BL-ARC002;
10. Prior organ transplantation or allogeneic hematopoietic stem cell transplantation;
11. Cumulative anthracycline dose \> 360 mg/m² from prior (neo)adjuvant anthracycline-based therapy;
12. Positive for human immunodeficiency virus (HIV) antibody, active tuberculosis, active hepatitis B virus infection, or active hepatitis C virus infection;
13. Active infection requiring systemic therapy;
14. Participation in another clinical trial within 4 weeks prior to the first dose;
15. Pregnant or breastfeeding women;
16. Subjects with claustrophobia or inability to lie flat for the duration of required examinations due to various reasons;
17. Any other conditions that, in the investigator's judgment, make the subject unsuitable for participation in this clinical trial.
