Risk Factors For Brain Metastases

The risk factor for developing brain metastases depends on the location and type of the primary tumor. Lung cancer poses the greatest risk of developing brain metastases followed by breast cancer, skin cancer, colon cancer and kidney cancer.

Lung Cancer. A more recent study revealed a 10.4% chance of brain metastases in lung cancer patients at the time of presentation and 91% of these patients develop brain metastases within a year of initial diagnosis. 20% of all detected brain metastases are metastatic lung cancer. Lung metastases are found even in the initial stage and non-symptomatic patients. The clinical factors that are thought to be higher risk factors for the development of brain metastases include non-squamous cell lung cancers, younger age and high tumor grade. Brain metastases drastically change the treatment protocol as well as limit the treatment intervention. Brain metastases of lung cancer have a very poor prognosis with survival rate of 4-6 months.¹

Breast Cancer. Breast cancer is the leading cause of cancer in women. Metastatic breast cancer is the second leading cause of brain metastasis after lung cancer, responsible for 10-15% of brain metastastic cases. The prognosis of patients with metastatic breast cancer to the brain is poor with a median survival rate of 7.5 months. There are higher chances of developing brain metastases in breast cancer patients with higher grade of tumor, HER2 positive, high Ki-67 and hormone receptor negative patients.^{2, 3}

Skin Cancer. Brain metastasis of melanoma is associated with poor prognosis. The primary characteristics that have a higher probability of developing into brain metastases include the location of melanoma on the scalp, nodular type, ulcerated, tumor depth of greater than 4 mm and stage of the tumor.⁴

Colon Cancer. The chances of developing brain metastases from colorectal cancer are rare and even if it develops, it develops at a later stage of the disease. The chances of survival of patients with brain metastases from metastatic colon cancer are around 32 months.⁵ The risk of developing brain cancer due to colon cancer increases with the addition diagnosis of rectal cancer, lung metastases and metachronous metastatic disease.⁶

Kidney Cancer. 1.2% cases of renal cancer can develop into brain metastases.⁷ The risk increases with increased tumor size >10 cm, N+ disease, clear cell histology, late stage disease and sarcomatoid differentiation of tumor. The prognosis with brain metastases remains poor.⁸

Brain metastasis is an unforeseeable outcome of certain cancers. The cancer that has spread from other body parts to the brain and has not primarily originated in the brain is known as brain metastases. It is interesting to note that primary brain tumors are rare and brain metastases is ten times more common that primary brain tumor. The tumor cells from other parts of the body can travel to the brain either directly via bloodstream or lymphatic system. These metastatic cells then grow in the brain leading to metastatic brain tumor. Of note, the tumors that have been metastasized into the brain are known by their primary source of cancer and not brain cancer, such as lung cancer metastasized to the brain will be known as metastasized lung cancer to the brain.⁹

The growing brain metastases can cause intracranial pressure by pressing into surrounding structures and in this manner can press into important structures leading to functional disruption depending on the location of the tumor, in addition to causing electrical abnormality in the motor as well as sensory signals in the brain. These functional and electrical disruptions can lead to certain signs and symptoms. Headache with or without nausea and vomiting is the most common symptom of a brain metastases due to the raised intracranial pressure. The other symptoms of brain metastases include seizures, dizziness, and changes in sensory perceptions, motor function changes, cognitive and behavioral changes, altered mental state, visual changes, along with depression. The presence of these symptoms depends on the location of the tumor.¹⁰ However, all these symptoms are not exclusive for brain metastases and thus make the diagnosis difficult for the examining physician.

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