Brain Metastasis: What Is It And What Is Its Treatment?

Brain metastasis is the most common brain tumor and is a challenge for clinicians. They constitute about 90% of all cases of brain tumors.

It is estimated that between 10 and 40% of cancer patients present with brain metastases ; its incidence is increasing given the higher average survival of cancer patients, thanks to current therapies.

Tumors have a different ability to metastasize in the brain and must have the ability to penetrate the blood-brain barrier, which is what covers and protects the brain.

Metastasis is a characteristic that cancer cells possess that consists of the ability to invade tissues both neighboring and distant from the first tumor. That is, cancer cells can migrate to other parts of the body and cause another tumor.

The symptoms of brain metastasis are varied and depend on the affected site, as do the associated risks of seizure.

Causes of brain metastasis

Brain metastasis generally occurs by hematogenous spread, that is, because cancer cells from the primary tumor pass into the blood, reach the brain, and spread.

In this sense, it is interesting that the distribution of brain metastases is proportional to the blood flow in the area in question, ranking according to the following percentages:

• 80% of lesions in the brain.
• 15% in the cerebellum.
• 5% in the brainstem.

The first step for cells to spread throughout the brain is for them to invade the arterial wall at the level of the first primary tumor. In this way, some cancer cells are allowed to break off and enter the bloodstream.

Then, the cell or cells that have passed into the blood must be able to adhere to the vessels of the brain, passing the blood-brain barrier.

The blood-brain barrier and the absence of a lymphatic system give the brain significant protection from the entry of many drugs and microorganisms, but it is eventually unable to prevent the entry of certain cells.

How do neoplastic cells cross the blood-brain barrier?

The mechanisms used by neoplastic cells to cross the blood-brain barrier are a matter of study. However, it has already been shown that there are at least two mechanisms :

• Paracellular, that is, to cross it between the barrier cells : for this, the cells have to destroy the junctions between the cells and they must have certain proteins and inflammatory mediators.
• Trans-cellular  or, what is the same, causing the direct death of the barrier cells.

What Happens After I Have Crossed the Blood Brain Barrier?

Once they are inside the brain, the cells pass into the microvasculature of the brain and from there they extravasculate, that is, they exit towards the tissue.

Survival and proliferation from that moment on is dependent on the ability to maintain an adequate supply of oxygen and nutrients, which explains why these malignant cells remain very close to the blood vessels.

Brain metastasis treatments

Within the usual treatment, if the patient suffers from a headache, an imaging study should be done in order to rule out complications that require surgical intervention.

Regarding the specific treatment of brain metastasis, we can mention the following options:

• Surgical resection : consists of the removal of the tumor through small incisions. It is done by vitrectomy. It has a series of advantages such as that it removes the effect of the mass, eliminates the source of edema and improves overall survival compared to holocranial radiotherapy alone.
• Holocranial radiation therapy : historically, it has been considered the treatment of choice when the tumor burden is high. It has also been shown to be useful as an adjunct to surgical treatment, significantly reducing the incidence of recurrences after resection.
• Stereotaxic radiosurgery : consists of focally administering radiation to the tumor. It has shown better survival and less recurrence in those patients with an injury; and also better local control, but not a significant difference in survival in those with 2 or 3 lesions.

• Chemotherapy: Brain metastases are often refractory to chemotherapy. However, the integration of new therapeutic alternatives, such as target agents and immune checkpoint inhibitors, have intensified research in this area.

Early diagnosis is key

Brain metastases make up about 90% of all brain cancer cases. It is essential to establish a diagnosis as early as possible to try to stop the progression of the disease.

Today, there are different treatments that are improving more and more. However, brain metastasis is a very aggressive cancer and much research remains to be done in this area.

Experts from the American Society of Clinical Oncology (ASCO) make more information available on how to help patients.