High-dose Furmonertinib in the Treatment in Patients With Advanced, Metastatic NSCLC With Progressed After First- or Second-line Treatment With Osimertinib

Inclusion Criteria: * Histologically or cytologically confirmed metastatic lung adenocarcinoma * Progression of imaging-confirmed extracranial lesions after first- or second-line treatment with Osimertinib * Previous genetic testing for a definite EGFR-sensitive mutation and imaging-confirmed extracranial lesion progression after first-line treatment with Osimertinib; or previous genetic testing for a definite T790M mutation and imaging-confirmed extracranial lesion progression after second-line treatment with Osimertinib. * Pre-existing clinical benefit after treatment with Osimertinib, including CR, PR, SD (duration \>6 months); * Patients with at least 1 measurable lesion according to the criteria for evaluating the efficacy of solid tumors (RECIST 1.1) * Normal functioning of major organs * Pre-menopausal women of childbearing potential with a negative serum or urine pregnancy test within 7 days prior to the first dose of the drug * Subjects volunteered and signed a written informed consent form. Exclusion Criteria: * Previous chemotherapy or immunotherapy * Patients with non-lung adenocarcinoma, including squamous lung cancer or mixed histological types * Progression of imaging-confirmed extracranial lesions after prior Osimertinib treatment with accessible treatment options after genetic testing * Patients with symptomatic brain metastases, meningeal metastases or spinal cord compression * Any unrecovered CTCAE \> grade 1 toxicity reaction following prior Osimertinib treatment at the start of study drug therapy * Other malignant tumors within 5 years or history of other malignant tumours; except effectively controlled basal cell carcinoma of the skin, carcinoma in situ of the uterine cervix, ductal carcinoma in situ of the breast, papillary carcinoma of the thyroid, superficial bladder tumors, etc. * History of interstitial pneumonia with previous diagnosis * Other circumstances that, in the judgement of the investigator, make them unsuitable for inclusion in the study