Inclusion Criteria:
* Patients who have signed informed consent and agree to comply with the protocol.
* Age ≥ 18 years.
* Histologically or cytologically confirmed relapsed small-cell lung cancer after failure of platinum-based chemotherapy and PD-1/PD-L1 monoclonal antibody treatment.
* At least one measurable lesion according to RECIST v1.1.
* ECOG performance status 0 or 1.
* Expected survival time ≥ 3 months.
* Recovery of prior anti-tumor therapy toxicities to ≤ Grade 1 (NCI-CTCAE v5.0), except alopecia, fatigue, hyperpigmentation, and stabilized thyroid dysfunction (on hormone replacement) as specified in protocol.
* Adequate cardiac function: left ventricular ejection fraction (LVEF) ≥ 50%.
* Adequate organ function: ANC ≥ 1.5×10\^9/L, platelets ≥ 100×10\^9/L, hemoglobin ≥ 90 g/L.
* Total bilirubin ≤ 1.5×ULN (≤ 3×ULN if liver metastases); AST and ALT ≤ 2.5×ULN (≤ 5.0×ULN if liver metastases).
* Creatinine ≤ 1.5×ULN or creatinine clearance ≥ 50 mL/min (Cockcroft-Gault).
* INR ≤ 1.5; APTT ≤ 1.5×ULN.
* Women of childbearing potential: negative pregnancy test within 7 days before first dosing and non-lactating.
* Effective contraception from screening through 6 months after end of treatment for all patients with reproductive potential.
Exclusion Criteria:
* History of hypersensitivity to paclitaxel micelles, ivonescimab (YS11/YS), or components of these investigational products, or structurally related agents.
* Prior systemic therapy with taxanes and/or anti-VEGF monoclonal antibodies.
* Major surgery within 28 days before first investigational treatment.
* Antitumor treatment within 4 weeks (or 5 half-lives for biologics, whichever is shorter), including chemotherapy, targeted therapy, biologics, immunotherapy, curative radiotherapy, major surgery, or large-field radiotherapy; small-molecule targeted therapy within 5 days before first dose (as protocol details).
* Use of CYP3A/CYP2C inhibitors or inducers within 7 days before first dose, or need to continue during study.
* Use of traditional Chinese anti-tumor herbal medicines within 7 days before first dose, or need to continue during study.
* Ongoing use of drugs known to prolong QT interval or induce torsades during study.
* Symptomatic CNS involvement (including symptomatic brain metastases); brain-metastasis patients previously on steroids must be tapered and off steroids for ≥14 days unless protocol allows exceptions.
* Uncontrolled pleural effusion, pericardial effusion, or ascites requiring repeated drainage.
* Tumor encasement/invasion of major thoracoabdominal/other vital vessels judged unsafe for protocol treatment.
* Clinically significant bleeding within 3 weeks before informed consent (e.g., hemoptysis, GI bleeding, bleeding ulcer).
* Inflammatory bowel disease, major bowel resection history, immune-related colitis, bowel obstruction, chronic diarrhea, or Gilbert syndrome.
* Other malignancy within 5 years, except adequately controlled basal cell carcinoma, cervical CIS, or DCIS \>3 years.
* Serious cardiac/cerebrovascular disease: NYHA class ≥2 heart failure, acute coronary syndrome within 6 months, or stroke/TIA/hemorrhagic stroke within 6 months.
* Significant arrhythmia (complete LBBB, third-degree AV block, uncontrolled ventricular/atrial arrhythmia; stable controlled arrhythmia exceptions may apply).
* Active unstable thromboembolic disease requiring treatment within 6 months (except \>4-week old peripheral line thrombosis).
* Uncontrolled systemic diseases likely to interfere with protocol conduct, including uncontrolled hypertension, diabetes, active bleeding, active hepatitis B/C/HIV (including HBV DNA \>10000 copies/mL when HBsAg positive), or other active infection.
* Autoimmune disease requiring systemic treatment in prior 2 years (excluding replacement hormones).
* Current or clinically significant history of ILD, or ILD/grade ≥2 radiation pneumonitis.
* Severe neurologic or psychiatric disease.
* Unhealed wound, ulcer, or fracture within 4 weeks before informed consent.
* Planned or received live vaccine within 28 days before randomization/first dose.
* Pregnancy or breastfeeding.
* Any other condition the investigator judges to make trial participation inappropriate.
