Metastatic brain tumors are the most common type of brain tumor found in adults. These tumors arise as a result of cancer that has spread from another part of the body. Today, advanced diagnostic techniques that detect cancer while it is still in the initial stages means cancer can often be treated before it spreads. However, brain metastasis is still one of the most common complications of cancer, with around 170,000 individuals diagnosed with the condition every year in the United States.
Estimates suggest that about 10% to 20% of all brain metastases are single tumors, with the remainder arising as multiple tumors. Nearly 85% of the tumors are found in the cerebrum, which is the largest part of the brain, and the other 15% are found in the cerebellum. The incidence of brain metastasis increases with age and starts to rise among those aged between 45 and 64 years of age. The highest rates of disease occur in those aged 65 years and older.
Studies show that cancer cells break away from the primary tumor and enter the circulatory system or blood stream. The cells then use the circulatory system to migrate to other organs in the body. Initially, they move into the lungs and, from there, they migrate towards other organs such as the brain. Some research suggests these cancer cells can separate from the primary tumor even in the earliest stages of cancer. When these circulating cancer cells enter a new organ, they may lie dormant or rapidly divide and give rise to a secondary tumor.
Types of brain metastasis
Depending on the type of primary cancer, the cells that break away will affect different organs first. For example, since the lungs send blood to the brain, lung cancer can spread quickly to the brain. Colon cancer tends to spread to the liver and lungs, while breast cancer eventually involves the bones, lungs and brain. Examples of the types of cancer that spread to the brain include:
- Lung cancer
- Breast cancer
- Genitourinary cancer
- Bone cancer or osteosarcoma
- Skin cancers or melanomas
- Head and neck cancers
- Pancreatic cancer
The symptoms of a metastatic brain tumor are similar to those seen with primary brain tumors and depend on where the tumor is located in the brain. Some of the common symptoms include:
- Headaches – These may be caused by swelling (edema) due to leakage from the tumor’s blood vessels or due to intracranial pressure caused by tumor growth.
- Seizures – These may arise due to disrupted electrical activity in the brain caused by the tumor.
- A metastatic brain tumor can also cause cognitive changes and affect memory, behavior and personality.
- Motor difficulties may also arise, causing weakness and problems with balance.
- Tumors that have spread to the spinal cord may cause back pain, numbness, altered sensation in the limbs and incontinence.
Reviewed by Sally Robertson, BSc