This study adopts a retrospective design. Patients enrolled will include those who received furmonertinib (treatment duration ≥1 month) between March 3, 2021, and December 31, 2024, with concurrent therapies permitted (e.g., radiotherapy, intrathecal chemotherapy, surgical interventions such as ventriculoperitoneal shunting). A retrospective analysis will be conducted to investigate the efficacy and safety of furmonertinib-based therapy (with or without other treatments) in EGFR-mutated NSCLC patients with leptomeningeal metastasis.

Inclusion Criteria:

1. Patients aged ≥18 years, male or female;
2. Histologically or cytologically confirmed diagnosis of **non-small cell lung cancer (NSCLC);
3. " EGFR mutation-positive"(classic or non-classic mutations) confirmed by genetic testing;
4. "Leptomeningeal metastasis" definitively diagnosed by investigators based on "EANO-ESMO diagnostic criteria", involving comprehensive clinical assessment including symptom evaluation, imaging evaluation (MRI/CT), and/or cerebrospinal fluid (CSF) cytology;
5. Received furmonertinib (treatment duration ≥1 month) between "March 3, 2021, and December 31, 2024", with concurrent therapies permitted (e.g., radiotherapy, intrathecal chemotherapy, surgical interventions such as ventriculoperitoneal shunting).

Exclusion Criteria

1. History of other malignancies during NSCLC treatment or prior to diagnosis, except those effectively controlled (e.g., complete remission ≥5 years);
2. Severe gastrointestinal disorders affecting drug administration or absorption, including but not limited to peptic ulcer disease, inflammatory bowel disease, or malabsorption syndromes;
3. Evidence of uncontrolled systemic diseases (e.g., uncontrolled hypertension [BP >140/90 mmHg despite treatment], diabetes mellitus [HbA1c >8%], arrhythmias, heart failure [NYHA class III/IV], active bleeding, active infections requiring IV antibiotics, or interstitial pneumonia requiring corticosteroid therapy), which in the investigator's judgment may directly compromise patient prognosis;
4. Incomplete medical records or follow-up data;
5. Pregnancy or lactation;
6. Other severe acute/chronic medical conditions, psychiatric disorders, or laboratory abnormalities that, in the investigator's opinion, may confound the interpretation of study results.

Patients with EGFR-mutated non-small cell lung cancer (NSCLC) and leptomeningeal metastasis who received furmonertinib therapy between **March 3, 2021, and December 31, 2024**, with a treatment duration of ≥1 month.