A shadow on the brain after one year of chemotherapy for small cell lung cancer may be a brain metastasis of lung cancer, but further tests such as MRI are still needed to confirm the diagnosis. Brain is a common metastatic site of lung cancer, especially small cell lung cancer. When lung cancer spreads to the brain, it will show up as a shadow on the brain during examination and headache, dizziness, nausea, vomiting or other neurological symptoms. Typically, cancer cells enter the brain through the bloodstream route. Since the skull is a closed structure, the growth of the tumor will inevitably compress the brain tissue and limb movement disorders or cancerous meningitis may occur. Patients will experience increased intracranial pressure and exhibit symptoms such as lethargy, apathy, nausea, headache, and in a few cases even epileptic symptoms. Patients will also gradually develop headaches, nausea and more severe symptoms. Most headaches are severe and painful and are prone to fever. When small cell lung cancer gradually metastasizes to the brain, there is also a more pronounced impairment of vision. This is because when intracranial pressure rises, venous return to the eye is blocked, leading to blood stasis, edema and damage. If there is a shadow on the brain after chemotherapy for lung cancer, patients are advised to immediately seek medical treatment for further examination, and after clarifying the cause of the disease, they must receive systematic and standardized treatment under the guidance of doctors as early as possible to avoid deterioration of the disease.