HF50 for HER2-positive and HER2-low advanced solid tumors

Inclusion Criteria:

* Participants must voluntarily provide written informed consent (ICF) prior to any study-related procedures, and be capable of complying with all protocol requirements.
* Adult participants aged between 18 and 75 years (inclusive) at the time of ICF signing.
* Histologically or cytologically confirmed advanced HER-2 positive or HER-2 low-expression solid tumors that are unresectable, metastatic, or have relapsed after standard therapies, are intolerant to standard therapies (e.g., chemotherapy, targeted therapy), or lack effective treatment options.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
* Life expectancy of at least 3 months.
* At least one measurable lesion as defined by RECIST version 1.1.
* Adequate organ and bone marrow function as demonstrated by the following laboratory parameters:Hematologic Function:Absolute neutrophil count (ANC) ≥1.5×10⁹/L、Lymphocyte count ≥1.0×10⁹/L、Platelet count ≥90×10⁹/L、Hemoglobin ≥9.0 g/dL (without transfusion or erythropoietin-stimulating agents within 14 days)； Coagulation Parameters:Activated partial thromboplastin time (aPTT) ≤1.5×ULN、 International normalized ratio (INR) ≤1.5. Hepatic Function:Total bilirubin (TBIL) ≤1.5×ULN、Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5×ULN (≤5×ULN for participants with liver metastases, and TBIL ≤3×ULN)； Renal Function:Creatinine clearance (CrCl) ≥50 mL/min (Cockcroft-Gault formula).
* Female participants of childbearing potential must have a negative serum pregnancy test at screening and prior to the first dose. Male and female participants of childbearing potential must agree to use effective contraception during the study and for 6 months after the last dose.

Exclusion Criteria:

* History of active autoimmune disease or autoimmune disease considered unsuitable for study participation, with exceptions for localized skin conditions (e.g., eczema involving \<10% of body surface area, vitiligo, psoriasis, alopecia) or childhood asthma resolved without treatment in adulthood.
* Current use of immunosuppressants or systemic corticosteroids (\>10 mg/day prednisone or equivalent) within 4 weeks prior to the first dose, except for local steroid use.
* Receipt of systemic chemotherapy, radiotherapy, targeted therapy, or immunotherapy less than 2 weeks (or 4 weeks for nitrosourea or mitomycin C) or within 5 half-lives of the prior therapy before the first dose.
* Symptomatic brain metastases or leptomeningeal disease unless adequately treated (e.g., surgery or radiotherapy) with no evidence of progression for ≥28 days and off systemic steroids for ≥14 days prior to the first dose.
* Unresolved toxicities from prior therapies ≥Grade 2 (CTCAE v5.0) at baseline, except for toxicities deemed by the investigator to pose no safety risk (e.g., alopecia, stable hypothyroidism with hormone replacement).
* Significant cardiovascular or cerebrovascular conditions, including but not limited to:Thromboembolic events requiring therapeutic anticoagulation within 3 months prior to the first dose.NYHA Class III or IV heart failure.Acute coronary syndrome, congestive heart failure, aortic dissection, or stroke within 6 months prior to the first dose.Uncontrolled hypertension (systolic blood pressure \>160 mmHg or diastolic blood pressure \>100 mmHg), unless controlled with antihypertensive medication.
* Active infection or unexplained fever \>38.5°C within 1 week prior to the first dose (tumor-related fever may be eligible at the investigator's discretion).
* Known HIV infection, active hepatitis B virus (HBV) infection (HBV DNA \>ULN), or active hepatitis C virus (HCV) infection (HCV RNA \>ULN).
* Gastrointestinal symptoms or other conditions requiring intervention within 4 weeks prior to the first dose that would, in the investigator's judgment, impair study participation.
* Pregnant or breastfeeding women.
* Any other severe systemic disease, psychological condition, or significant clinical abnormality deemed unsuitable for study participation by the investigator.