The primary objective is to evaluate the safety and tolerability of RC278; determine the maximum tolerated dose (MTD) and/or maximum administered dose (MAD) of RC278; and determine the recommended phase 2 dose (RP2D)， and assess the efficacy of RC278 at the RP2D dose;

Inclusion Criteria:

1. Voluntarily participate in this study, sign the informed consent form, and be able to adhere to the study protocol;
2. Age between 18 and 75 years (including 18 and 75 years);
3. ECOG PS score of 0 or 1;
4. Expected survival ≥12 weeks;
5. According to RECIST v1.1 criteria, based on imaging examinations, there is at least one measurable target lesion;
6. Sufficient bone marrow, liver, kidney, and blood clotting function

Exclusion Criteria:

1. Pregnant, breastfeeding, or intending to become pregnant subjects.
2. Subjects with brain metastases.
3. Subjects with unresolved toxicities from prior anti-tumor therapy not recovered to NCI-CTCAE v5.0 Grade 1.
4. Subjects with known hypersensitivity or delayed allergic reactions to any component of the investigational drug or similar drugs.
5. Subjects with acute, chronic, or symptomatic infections.
6. Subjects with uncontrolled cardiovascular diseases.
7. Subjects with confirmed or suspected interstitial lung disease (ILD), drug-related pneumonia, radiation pneumonitis, severely impaired pulmonary function, or other pulmonary diseases.
8. Subjects with a history of cirrhosis (Child-Pugh B or C class).
9. Subjects with active inflammatory bowel disease.
10. Subjects with uncontrolled diabetes (HbA1c ≥ 10%).
11. Subjects who experienced arterial/venous thromboembolic events, deep vein thrombosis, pulmonary embolism, or stroke within 6 months prior to the first dose.
12. Subjects with pericardial effusion or cardiac tamponade, or third-space fluid accumulation, which, in the investigator's judgment, cannot be controlled or stabilized by drainage or other methods.
13. Subjects with active autoimmune diseases requiring systemic treatment within the past 2 years.
14. Subjects with a history of other invasive malignancies within 5 years prior to the first dose, or evidence of residual disease from a previously diagnosed malignancy.
15. Subjects with a history of other acquired or congenital immunodeficiency diseases or organ transplantation.
16. Subjects with a history or current diagnosis of uncontrolled psychiatric disorders.
17. Subjects with poor adherence, who are unlikely to comply with the trial procedures.
18. Subjects with any other diseases, metabolic abnormalities, physical examination abnormalities, or laboratory abnormalities, which, in the investigator's judgment, raise suspicion of an underlying condition making the subject unsuitable for the investigational drug, or which may affect the interpretation of the study results, or place the subject at high risk.