During a brain biopsy, a neurosurgeon removes a small sample of brain tissue through a small hole in the skull. The tissue will then be examined under a microscope, in order to determine the type of cells causing the cancer.

Patients with metastatic brain cancer from a cancer in another part of the body usually do not require a brain biopsy. Sometimes a brain tumor biopsy is the first evidence that there is cancer in another organ, such as the lung, prostate or breast.