This is a prospective, single-center, open-label investigator-initiated study designed to evaluate the safety, tolerability, radiation dosimetry, biodistribution, and preliminary antitumor activity of [177Lu]Lu-RTX-2358 in combination with immune checkpoint inhibitors (ICIs) in patients with fibroblast activation protein (FAP)-positive metastatic non-small cell lung cancer (NSCLC). Eligible participants will receive one or two cycles of [177Lu]Lu-RTX-2358 followed by standard PD-1 inhibitor therapy. Safety, tumor response, biodistribution, radiation dosimetry, and survival outcomes will be evaluated throughout treatment and follow-up.

Inclusion Criteria:

Written informed consent obtained before any study procedures. Age ≥18 years. Histologically or cytologically confirmed metastatic NSCLC. FAP-positive disease demonstrated by FAPI PET imaging. At least one measurable lesion according to RECIST version 1.1. ECOG performance status of 0-1. Estimated life expectancy of at least 3 months. Adequate bone marrow, hepatic, renal, and coagulation function. Willing to comply with radiation protection requirements. Willing to use highly effective contraception during and after study treatment.

Exclusion Criteria:

• History of another active malignancy requiring treatment within 2 years before the first administration of [177Lu]Lu-RTX-2358, except adequately treated basal cell carcinoma of the skin or carcinoma in situ treated with curative intent.

Symptomatic brain metastases or central nervous system metastases requiring active treatment. Participants with previously treated brain metastases are eligible if the disease has remained clinically and radiographically stable for at least 24 weeks.

Symptomatic spinal cord compression or radiographic evidence of impending spinal cord compression.

Major surgery, open biopsy (excluding needle biopsy), or significant traumatic injury within 4 weeks before the first administration of [177Lu]Lu-RTX-2358.

Prior treatment with any radioligand therapy or therapeutic radiopharmaceutical.

Receipt of systemic anticancer therapy, including chemotherapy, immunotherapy, targeted therapy, biologic therapy, investigational agents, or antitumor traditional Chinese medicine, within 21 days before the first administration of [177Lu]Lu-RTX-2358, unless the protocol-defined washout period has been satisfied.

Receipt of curative radiotherapy within 6 weeks before the first administration of [177Lu]Lu-RTX-2358. Palliative radiotherapy is permitted if completed at least 2 weeks before treatment, involves less than 10% of bone marrow, and does not include target lesions.

Unresolved toxicities from previous anticancer therapy greater than Grade 1 according to NCI CTCAE version 5.0, except stable chronic toxicities judged by the investigator not to pose a safety risk (e.g., alopecia, peripheral neuropathy, or fatigue).

Endocrine dysfunction involving the thyroid, adrenal, pituitary, or pancreas that would preclude treatment with immune checkpoint inhibitors.

Known interstitial lung disease, immune-related pneumonitis, pulmonary fibrosis, or active pulmonary fibrosis.

Severe urinary incontinence, hydronephrosis, bladder outlet obstruction, or other clinically significant urinary tract disorders that may interfere with radiopharmaceutical clearance.

Clinically significant cardiovascular disease, including myocarditis, pericarditis, myocardial infarction, unstable angina, New York Heart Association Class III or IV heart failure, uncontrolled arrhythmias, uncontrolled hypertension, or conditions associated with clinically significant QT interval prolongation within 6 months before enrollment.

Active uncontrolled infection, including human immunodeficiency virus (HIV) infection, active hepatitis B or hepatitis C infection, active syphilis, or any infection requiring systemic therapy that is not adequately controlled.

Serious or non-healing wounds, active ulcers, or fractures requiring ongoing treatment.

Severe psychiatric illness or any medical condition that, in the investigator's judgment, would compromise participant safety, interfere with study participation, or affect protocol compliance.

Pregnant or breastfeeding women. Known hypersensitivity to [177Lu]Lu-RTX-2358 or any of its components. History of significant occupational exposure to ionizing radiation exceeding applicable regulatory limits.

Participation in another interventional clinical trial within 4 weeks before screening.

Inability or unwillingness to undergo required study procedures, including PET/CT, SPECT/CT, CT/MRI examinations, or inability to comply with protocol requirements.

Any other condition that, in the investigator's judgment, would make the participant unsuitable for participation in this study.