Aumolertinib Combined Intrathecal Chemotherapy for Leptomeningeal Metastasis From EGFR-Mutated NSCLC and Prognostic Value of Dynamic Changes in cfDNA Profiles

Inclusion Criteria: * Age at least 18 years old. * The Eastern Cancer Organization Collaboration Group (ECOG) had a physical fitness score of 0 to 3, and had not worsened in the previous 2 weeks, with a minimum expected survival of 12 weeks. * NSCLC confirmed by histology or cytology, positive cerebrospinal fluid cytology, and combined with central nervous system function and brain imaging findings, diagnosed as NSCLC with meningeal metastasis (including advanced patients who had relapsed or were initially diagnosed after previous surgical treatment; GPA is recommended for grading and typing in the diagnosis of meningeal metastasis from lung cancer). * Tumor tissue samples or blood samples were tested and confirmed as EGFR sensitive mutations (including exon 19 deletion or L858R, both alone or coexisting with other EGFR site mutations). The first choice is to submit tumor tissue for examination; If the tumor tissue is inaccessible or the subject is not eligible for tissue biopsy, a blood sample may be sent for examination. * The patient has implanted an Ommaya capsule; * CT examination of clinical symptom areas (spine and/or brain) and/or head within the past 3 months to rule out contraindications to cerebrospinal fluid examination; * The subjects agreed to provide two cerebrospinal fluid samples (before treatment and within one week after disease progression) for genetic testing; * Women of childbearing age need to take appropriate contraceptive measures and should not breastfeed three months after screening and discontinuing study treatment. "Before starting administration, the pregnancy test was negative, or one of the following criteria was met to demonstrate that there was no risk of pregnancy: 1. Postmenopause is defined as amenorrhea at least 12 months after age greater than 50 years and cessation of all exogenous hormone replacement therapy. 2. Women younger than 50 years of age may also be considered postmenopausal if they have amenorrhea for 12 months or more after stopping all exogenous hormone therapy, and their luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels are within the laboratory postmenopausal reference values. 3. Have undergone irreversible sterilization surgery, including hysterectomy, bilateral ovariectomy, or bilateral salpingectomy, except for bilateral tubal ligation. * Male subjects should use barrier contraception (i.e., condoms) three months after screening and discontinuation of study treatment. * The subject voluntarily participated and signed an informed consent form in writing. Exclusion Criteria: * Have received any of the following treatments: 1. Within 4 weeks before the first administration of the investigational drug, the subject had undergone major surgery (such as craniotomy, thoracotomy, or laparotomy). The definition of major surgical surgery refers to Level 3 and Level 4 surgery specified in the "Management Measures for Clinical Application of Medical Technology" implemented on November 1, 2018; 2. Within 7 days before the first administration of the study drug, a strong CYP3A4 inhibitor, inducer, or CYP substrate (CYP2C8, CYP2D6, etc.) was used. 3. Subjects with other malignant tumors, excluding basal cell carcinoma of the skin and carcinoma in situ. * At the beginning of the study treatment, there was a residual toxicity greater than CTCAE level 3 that could not be alleviated from previous treatment. * There are pleural effusion/peritoneal effusion requiring clinical intervention (patients who do not require drainage of the effusion or who have been stable for 2 weeks or more after drainage can be enrolled); Presence of pericardial effusion (small amounts of pericardial effusion that are stable for 2 weeks or more are allowed to be included in the group). If local use (such as thoracic perfusion) of anti-tumor drugs is used during drainage, and at least 5 drug half-lives or 21 days (whichever is shorter) must be eluted before the first administration of the study treatment before enrollment; * Subjects are unwilling to provide cerebrospinal fluid samples or clinical information; * Subjects have contraindications for cerebrospinal fluid examination; * Previously or currently suffering from primary malignant tumors of the central nervous system; * Suffering from autoimmune or inflammatory diseases of the central nervous system (not limited to multiple sclerosis, neurosarcoidosis, chronic fungal, rickettsial, or bacterial meningitis); * Subjects who are allergic to the MRI contrast agent gadolinium or who cannot tolerate MRI examination (such as having a cardiac pacemaker, having metal in their body, etc.). * According to the judgment of the researcher, there are any serious or poorly controlled systemic diseases, such as poorly controlled hypertension, active hemorrhagic constitution, or active infection. There is no need to screen for chronic diseases. * Clinically severe gastrointestinal dysfunction may affect the intake, transportation, or absorption of drugs, such as inability to take orally, uncontrollable nausea or vomiting, a history of extensive gastrointestinal resection, untreated recurrent diarrhea, atrophic gastritis, untreated stomach diseases requiring long-term administration of mass pump inhibitors, Crohn's disease, ulcerative colitis, and so on. * Hepatic encephalopathy, hepatorenal syndrome, or cirrhosis. * Meet any of the following cardiac examination results: 1. The mean value of the QT interval (QTcF) corrected by Fridericia's formula from three electrocardiogram (ECG) examinations at rest is\>470 msec; 2. resting ECG indicates conduction or ECG morphological abnormalities (such as complete left bundle branch block, 3rd degree atrioventricular block, 2nd degree atrioventricular block, and PR interval\>250 msec); 3. The presence of any factors that increase the risk of QTc prolongation or arrhythmia events, such as heart failure, hypokalemia, congenital long QT syndrome, a family history of long QT syndrome, or any concomitant medication that causes unexplained sudden death or prolongs the QT interval in immediate family members under the age of 40; 4. Left ventricular ejection fraction (LVEF)\<50%. * Insufficient bone marrow reserve or organ function, reaching any of the following laboratory limits (no corrective treatment within 1 week before laboratory examination and blood sampling): 1. Absolute neutrophil count\<1.5 × 109 / L； 2. Platelet count\<100 × 109 / L； 3. Hemoglobin\<90 g/L (\<9 g/dL); 4. If there is no clear liver metastasis, alanine aminotransferase is\>3 times the upper normal limit (ULN); If there is liver metastasis, alanine aminotransferase\>5 × ULN； 5. If there is no clear liver metastasis, aspartate aminotransferase\>3 × ULN； If there is liver metastasis, aspartate aminotransferase\>5 × ULN； 6. If there is no clear liver metastasis, total bilirubin\>1.5 × ULN； Or presence of Gilbert syndrome (unconjugated hyperbilirubinemia) or liver metastasis with total bilirubin\>3 × ULN； 7. Creatinine\>1.5 × ULN and creatinine clearance\<50 mL/min (calculated using the Cockcroft Gault formula); Only when creatinine\>1.5 × It is only necessary to confirm the creatinine clearance rate at ULN; 8. Serum albumin (ALB)\<28 g/L. * Active fungal, bacterial, and/or viral infections that require systemic treatment. * Female subjects who are pregnant, nursing, or planning to become pregnant during the study period. * Have a history of interstitial lung disease, a history of drug-induced interstitial lung disease, a history of radiation pneumonia requiring steroid treatment, or any evidence of clinically active interstitial lung disease. * A history of hypersensitivity to any active or inactive component of aumolertinib, or to drugs with a chemical structure similar to or in the same category as aumolertinib. * Patients who are allergic to or contraindicated to pemetrexed. * Any serious or uncontrolled ocular lesions (especially severe dry eye syndrome, dry corneal conjunctivitis, severe exposure keratitis, or other diseases that may increase epithelial damage) that, in the judgment of a doctor, may increase the safety risk of the subject; Or eye abnormalities that require surgery or are expected to require surgical treatment during the study period. * Subjects who, according to the judgment of the investigator, may have poor compliance with the research procedures and requirements, such as having a clear history of neurological or mental disorders (including epilepsy or dementia), or currently suffering from mental disorders. * The investigator determines that there are any conditions that endanger the safety of the subject or interfere with the evaluation of the study, or other conditions that the researcher believes are not suitable for enrollment.