On the one hand, the occurrence of brain metastasis means that the tumour cells from the primary lesion have spread and may metastasise to multiple sites throughout the body at the same time, and patients are likely to develop systemic tumour complications, including neurological symptoms. On the other hand, the tumour grows in an expansive manner within the skull. The growth process will compress the brain tissue and block the cerebrospinal fluid circulation pathway, thus causing intracranial hypertension symptoms, such as headache, nausea and vomiting.
If the tumor continues to progress, the brain tissue will be compressed and displaced, resulting in symptoms such as impaired movement of limbs or impaired consciousness, or in severe cases, brain herniation. There is also the fact that drug treatment is less effective after the occurrence of brain metastases. The existence of a blood-brain barrier in the brain tissue makes it difficult for general chemotherapy drugs to enter the brain.