Tumors that have spread to the brain from a primary neoplasm in other organs are metastatic brain tumors. Some of the most commonly treated intracranial brain tumors, these tumors are a complication of systemic cancers and an important cause of both morbidity and mortality in patients.
About 200,000 new brain metastases cases are diagnosed in the US annually, with the number growing with improved diagnostic techniques and awareness. Also, improved chemotherapy treatments of systemic cancers (malignancies) are causing longer patient survival but failing to protect the brain, leaving it vulnerable to the spread of tumors.
Basically any systemic malignancy can metastasize to the brain, although there are some with a greater proclivity to do so. Melanoma often metastasizes to the brain. Other malignancies such as lung, breast, renal and colon cancers are also frequently encountered. Metastatic brain tumors tend to be more common in adults than in children but occur equally in each gender.
Certain differences are seen in the types of primary malignancies responsible for the brain metastasis in the two genders. Lung cancer is the most common source of brain metastasis in males, but breast cancer is most common in females.
Besides the following, many can experience additional complications caused by the original tumor and its related manifestations.
- Increased Intracranial Pressure (ICP): Symptoms of brain metastases are often caused by the expansion of lesions and increased ICP (headache, vomiting and disturbance of consciousness)
- Headache: The initial symptom in about 50% of brain tumor patients
- Vomiting: An occasional accompaniment to the headache. Far more common in children than in adults, being described as violent or “projectile” in some children.
- Alteration in Consciousness: Common experience of alterations in consciousness, including both the level of consciousness and/or its quality. A brain tumor can induce a wide spectrum of changes in mental status from subtle alterations in personality to states of profound and irretrievable coma.
- Seizures (Epileptic Seizures/Fits): Associated with brain tumors in almost 35% of patients. Age increases the risk of epilepsy caused by a tumor especially in individuals 45+ years old.
- Focal (Specific) Neurological Symptoms: Certain symptoms are associated with tumors that occur in specific locations. These focal neurological symptoms affect the side of the body opposite from the side where a tumor is and can include different modalities of sensation like tingling and motor changes (hemiparesis).
Brain metastasis can be diagnosed utilizing the following tests:
- Computed Axial Tomography (CAT Scan/CT)
- Magnetic Resonance Imaging (MRI)
- IIf a metastatic tumor is suspected, the treating neuro-oncologist or neurosurgeon can ask for further testing (Generally in the form of a CT with contrast of the chest, abdomen and pelvis and a bone scan). These tests allow detection of a primary neoplasm elsewhere in the body. Additional testing can be indicated at times, but this constitutes the basic palette of tests.
Varies with the size and type of the tumor, the primary malignancy site, its extent locally and in the rest of the body (staging), the general health of the individual, and presence of other significant medical issues. Some of the goals of treatment can be to obtain a clear tissue diagnosis, relieve symptoms, improve functioning, and control the cancer and its satellite tumor within the brain.
At times, a tissue diagnosis is critical and can have occurred if the patient has a previously known malignancy. It can be obtained by a biopsy or removal at the site of the primary cancer. Alternatively, a metastatic brain tumor biopsy can be performed. If it is large and causing significant pressure, it can be removed to relieve pressure while providing adequate diagnosis tissue.
After obtaining a clear diagnosis of the brain tumor, staging of the systemic cancer is completed. After the patient’s medical condition stabilizes, a multidisciplinary team of physicians will discuss the options to maximize control and possible eradication of the tumor while minimizing morbidity or risk to the patient.
Three critical components of managing patients with metastatic brain tumors are non-chemotherapeutic and chemotherapeutic drugs, surgery to remove the tumor while avoiding brain damage or injury, and radiation.
- Non-chemotherapeutic drugs given to relieve pain like headache, control epilepsy, and diminish edema of the tumor. Chemotherapeutic drugs can also be provided to attack and kill cells that divide rapidly (like cancer cells). Also, chemotherapy can treat the entire brain while treating multiple cancer sites simultaneously.
- Surgery: Increasingly sophisticated neurosurgical techniques, navigation systems with intraoperative MRI, and improving anesthetic techniques allow neurosurgeons to remove metastatic brain tumors with minimal/acceptable morbidity and almost death or mortality risk. This gives tissue for diagnosis and improves control of the cancer, helping doctors use additional treatments in the brain. It also allows the oncologist to continue additional treatments that aim to control the systemic disease. Surgery is performed when the treating physician determines that it is likely to lead to greater symptomatic relief than might be achieved by other treatments and possibly extend survival.
- Radiation: like chemotherapy, radiotherapy can be provided through whole brain radiotherapy (WBRT) or fractionated doses. If there are less than four small (generally <3cm in diameter) tumors, then radiation can be administered in the form of precise, focused beams that target tumors while sparing surrounding tissue.
Radiation can also be administered after the surgical removal of a tumor, with the goal of exterminating residual malignant cells possibly located within the tumor resection bed (stereotactic radiosurgery). This is carried out through sophisticated machinery operated by an experienced neurosurgeon and radiation oncologist with careful input from a physicist. The primary advantage is its ability to treat lesions otherwise not easily treated surgically. It is also noninvasive, holds fewer risks, and results in shorter hospital stays. When there are more than 4 intracranial metastatic tumors, surgery or stereotactic radiosurgery have a smaller role in treatment. More global brain radiation treatments can be better suited for such situations. WBRT is administered in fractions over two to three weeks building up to the maximal and optimal effective dose. Administering the radiation in small fractions permits the normal brain to recover while tumor cells are killed.
Other types of treatment can be an option as well, as new trials for gene therapy are being carried out.
Many metastatic brain tumors have widespread tumor metastasis. The effectiveness of treatment of brain metastases is generally determined by how well the primary cancer is controlled. Without control over the primary cancer, treatment of metastatic brain tumors is a futile endeavor. The prognostic factors are complex and largely dependent upon the status of systemic disease, extent of neurological deficit, length of time between first diagnosis of cancer, and the diagnosis of brain metastasis, the type of primary tumor and the nature, size and invasiveness of the metastatic lesion, among other factors. Thus, careful coordination and communication between the neurosurgeon, radiation oncologist, and primary oncologist is essential. Relapse of disease either in the brain or the body is common and hence, frequent and consistent follow-up with imaging studies is also essential.