What Is a Brain Metastasis?
Brain metastases are secondary tumors that form when a primary cancer elsewhere in the body spreads to the brain through the bloodstream. They most often arise from lung cancer, breast cancer and melanoma; less frequently, kidney and colorectal cancers can also spread to the brain. Metastases are usually located in the cerebral hemispheres at the gray-white matter junction, and a substantial proportion of cases have multiple lesions. As advances in cancer treatment allow patients to live longer, the incidence of brain metastases has risen; it is therefore a picture seen more often today, but one whose management is steadily improving.
Symptoms and Diagnosis
Symptoms vary with the location and number of metastases: progressive headache (often worse in the morning), nausea and vomiting from raised intracranial pressure, location-dependent limb weakness or sensory loss, visual field loss, seizures, and cognitive and behavioral changes can occur. Contrast-enhanced brain MRI is the most sensitive method for diagnosis; metastases typically appear as well-defined, often ring-enhancing masses surrounded by edema and are frequently multiple. If the primary cancer is unknown, whole-body staging (PET-CT, chest-abdomen-pelvis CT) is performed. For a single lesion, surgical resection both provides a tissue diagnosis and removes the mass.
Single or Multiple? How the Decision Is Made
Treatment is planned by a team in which medical oncology, radiation oncology and neurosurgery work together. The first step is usually a steroid (dexamethasone) to reduce edema. For a limited number of metastases, local treatments come to the fore: surgical resection for a large, symptomatic lesion, and stereotactic radiosurgery (Gamma Knife, CyberKnife) for small-to-moderate or a few lesions. For more than five or widespread metastases, whole-brain radiotherapy may be considered alongside Gamma Knife; hippocampal-sparing techniques can be used to reduce cognitive side effects. Systemic treatment (chemotherapy, targeted agents, immunotherapy) is chosen according to the molecular profile of the primary cancer and plays an increasingly important role.
When Does Surgery Come to the Fore?
Surgical resection comes to the fore especially for a single, large, symptomatic or life-threateningly compressing metastasis; it both removes the mass and provides a tissue diagnosis, and it contributes to diagnosis when the primary cancer is unknown. A solitary metastasis in a reachable location, accompanying a controlled primary disease, is a suitable candidate for surgery. In surgery, neuronavigation, functional mapping and awake craniotomy when needed are used to preserve function. Radiosurgery to the tumor bed is often added after surgery. The decision is always multidisciplinary; our aim is to offer the patient the most appropriate combination of local and systemic treatment.
Prognosis and Realistic Expectations
The course in patients with brain metastases varies widely. Long-term control may be achievable with modern treatments in patients with a single metastasis, good performance status and a targetable molecular feature, whereas prognosis is more limited in patients with widespread disease and poor performance status. To estimate prognosis, tools that combine factors such as the type and molecular features of the primary cancer, the number of metastases, performance status and control of extracranial disease (DS-GPA) are used. Outcomes have improved markedly in recent years for cases that respond to targeted therapy and immunotherapy. We do not promise a guaranteed result; expectations are shared honestly.