Generally speaking, lung cancer metastasis to brain parenchyma survives 1-3 months if left untreated. With symptomatic and supportive treatment alone, survival may be 3-5 months. After standardized systemic treatment, cranial radiotherapy, targeted therapy, etc., the median survival is 10-12 months, or up to 3-5 years or longer. The prognosis is better after surgery, radiotherapy or targeted therapy for a single lesion. Patients with more lesions or those that grow in important areas such as the brainstem, where radiotherapy cannot raise the dose, have a relatively poor prognosis. The prognosis is even worse if meningeal metastases are present, with survival of 3-6 months. Small cell lung cancer 80% will eventually develop brain metastasis, and if eligible, brain prophylaxis irradiation is recommended, which can reduce the incidence of brain metastasis by 80%.