This study is designed as a prospective, multi-center investigation to explore the efficacy and safety of furmonertinib combined with upfront thoracic radiotherapy with or without metastatic lesion radiotherapy in subjects with EGFR-mutant NSCLC and malignant pleural effusion (MPE), aiming to provide additional evidence-based medical support for optimizing the management of NSCLC-MPE subjects. In addition, peripheral blood ctDNA next-generation sequencing (NGS) will be performed at two time points-before the first furmonertinib treatment and one month after the completion of thoracic radiotherapy-to identify subpopulations most likely to benefit from this therapeutic approach and to elucidate resistance mechanisms specific to the radiotherapy-plus-furmonertinib combination, ultimately facilitating more personalized care for these subjects.

This study is designed as a prospective, multi-center investigation that plans to enroll 63 subjects with stage IV non-small cell lung adenocarcinoma harboring EGFR-sensitive mutations (exon 19 deletion or exon 21 L858R mutation) complicated by malignant pleural effusions (MPE). Subjects will receive an initial 10-12 weeks of furmonertinib therapy with or without therapeutic thoracentesis to achieve adequate control of MPE, followed by thoracic radiotherapy targeting residual primary pulmonary lesions, regional lymph node metastases, and pleural metastatic lesions, with or without radiotherapy to osseous, adrenal, hepatic, or brain metastases (total irradiated sites ≤6, involved organs ≤3). For brain metastases, consolidative radiotherapy will be withheld if residual tumor diameter is <1 cm after furmonertinib treatment and no significant neurological symptoms are present.

1. Radiotherapy techniques: Depending on the availability at each participating center, subjects may receive one of the following modalities:

   • Intensity-modulated radiation therapy (IMRT),
   • Volumetric-modulated arc therapy (VMAT),
   • Stereotactic body radiation therapy (SBRT),
   • Stereotactic radiosurgery (SRS), or
   • Fractionated stereotactic radiosurgery (fSRS).

2. Prescription doses for primary and metastatic lesions: Based on institutional technical capabilities and the dose constraints of organs at risk in the radiotherapy plan, the following stereotactic or hypofractionated regimens are permissible:

   • Hypofractionated radiotherapy: DT 3000-4000 cGy/10 fractions, 3-4 Gy/fraction, once daily, 5 days/week;
   • SBRT: 27-50 Gy/3-5 fractions, 8-10 Gy/fraction, once daily, every other day;
   • SRS (for brain metastases): 20-24 Gy/fraction;
   • fSRS (for brain metastases): 27 Gy/3 fractions or 30 Gy/5 fractions.

Oral furmonertinib will be withheld before, during, and for 3 days after the completion of radiotherapy. Furmonertinib maintenance will be resumed 3 days after radiotherapy completion and continued until disease progression or unacceptable toxicity. We hypothesize that this treatment paradigm will effectively control MPE, significantly improve progression-free survival (and potentially overall survival), with manageable treatment-related toxicity.

Additionally, dynamic monitoring of peripheral blood ctDNA via next-generation sequencing (NGS) will be performed at two time points-before the first furmonertinib administration and one month after the completion of thoracic radiotherapy-to identify individuals most likely to benefit from this regimen and to elucidate resistance mechanisms to furmonertinib under the radiotherapy-plus-TKI combination, thereby informing clinical decision-making.

Inclusion Criteria:

1. Age ≥ 18 years.

2. Histologically or cytologically confirmed advanced lung adenocarcinoma.

3. Unlimited number of metastatic lesions, but with involvement of no more than 3 organs.

4. Previously untreated, clinical stage IV disease per AJCC/UICC 9th edition.

5. Presence of pleural effusion as indicated by chest CT or ultrasound; cytological confirmation of malignant cells in the pleural effusion is preferred. If malignant cells are not detected in the pleural effusion, chest CT with contrast or whole-body PET/CT must demonstrate unequivocal pleural nodular metastases.

6. After 8-10 weeks of furmonertinib therapy with or without therapeutic thoracentesis, the overall radiographic response is assessed as effective (CR + PR + SD), and malignant pleural effusion is adequately controlled (defined as no pleural effusion or only minimal pleural effusion on ultrasound or chest CT: maximum depth < 3 cm, estimated volume < 500 mL). Concurrent minimal pericardial effusion is permissible (defined as maximum diastolic width < 1 cm on echocardiography, estimated volume < 100 mL).

7. No prior thoracic radiotherapy.

8. Positive for EGFR-sensitive mutations (exon 19 deletion or exon 21 L858R).

9. No prior systemic anticancer therapy.

10. ECOG performance status 0-2, with a life expectancy of ≥ 12 weeks.

11. At least one measurable lesion per RECIST 1.1.

12. Adequate bone marrow function to tolerate anticancer treatment: WBC ≥ 3 × 10⁹/L, Hb ≥ 80 g/L, PLT ≥ 75 × 10⁹/L, and absolute neutrophil count (NEUT) ≥ 1.5 × 10⁹/L.

13. Essentially normal hepatic and renal function:

    1. Serum creatinine ≤ 1.5 × upper limit of normal (ULN) or creatinine clearance (CrCl) ≥ 50 mL/min;
    2. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 × ULN (≤ 5 × ULN is acceptable in patients with liver metastases);
    3. Total bilirubin (TBIL) ≤ 1.5 × ULN;
    4. Albumin ≥ 30 g/L and prealbumin ≥ 150 g/L.

14. Asymptomatic brain metastases.

15. Written informed consent obtained from all subjects.

Exclusion Criteria:

1. Pre-existing interstitial lung disease (ILD) or infectious fever prior to treatment.
2. Radiographic progression (PD) after 8-10 weeks of TKI therapy, or development of grade ≥ 2 ILD.
3. Concurrent autoimmune disease requiring long-term oral corticosteroid therapy.
4. Severe anemia.
5. Known hypersensitivity to furmonertinib.
6. Significant respiratory symptoms (e.g., chest tightness, cough) that preclude tolerance to radiotherapy.
7. Active hepatitis B or C virus infection with concomitant grade > 2 hepatic impairment. Patients may be considered eligible if liver function recovers to grade 1 after active hepatoprotective therapy and antiviral treatment.
8. Poorly controlled or continuously progressive pleural effusion after 8-10 weeks of furmonertinib therapy.
9. Symptomatic brain metastases.

Masking Description