Brain Metastases: Description and Treatment

04 January, 2020
Brain metastases usually occur by hematogenous dissemination. That is because the cancer cells of the primary tumor go into the blood and reach the brain where they spread.

Brain metastases are the most frequent kinds of brain tumors and they’re quite a challenge for doctors. In fact, they constitute about 90% of the total brain tumor cases.

Estimates indicate that between 10 and 40% of cancer patients have brain metastases. This is because their incidence is increasing, given the higher average survival of cancer patients, thanks to modern therapies.

Tumors have a different ability to metastasize in the brain and the ability to penetrate the blood-brain barrier, given that they use it to cover and protect the brain.

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

The clinical metastasis of the brain varies and depends on the affected area, as well as the associated risks of seizure.

Causes of brain metastases

An illustration of a brain.

Brain metastases usually occur by hematogenous dissemination. That is because the cancer cells of the primary tumor go into the blood, reach the brain, and spread.

In this regard, it’s interesting to note that the distribution of brain metastases is proportional to the blood flow of the area in question. It’s located according to the following percentages:

  • 80% of lesions in the brain
  • 15% in the cerebellum
  • 5% in the brain stem

The first step for the cells to spread through the brain is to invade the arterial wall at the level of the first primary tumor. This way some cancer cells can shed and enter the bloodstream.

Then, the cell or cells that made it into the blood have to be able to adhere to the vessels of the brain by trespassing the blood-brain barrier.

The blood-brain barrier and the absence of a lymphatic system give the brain significant protection against the entry of many drugs and microorganisms, but, eventually, it isn’t able to prevent the entry of certain cells.

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How does the blood-brain barrier cross the neoplastic cells?

A double illustration of a head and neurons.

The mechanisms used by neoplastic cells to cross the blood-brain barrier are worthy of studying. However, it’s already been shown that there are at least two mechanisms:

What happens after crossing the blood-brain barrier?

Once they’re inside the brain, the cells pass to the microvasculature of the brain and from there they are extravasated i.e. they head towards the tissue.

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

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Treatments for brain metastases

A person pointing at brain metastases in an X-ray.
With the usual treatment, if a patient suffers a headache, an imaging study should be done in order to rule out complications that would require surgical intervention.

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

  • Segmental resection: This one involves the removal of the tumor through small incisions. It’s done by vitrectomy and has a series of advantages such as being able to remove the effect of the mass, eliminate the source of edema, and improve overall survival compared to Holocraneana radiotherapy alone.
  • Holocranial radiotherapy: Historically, this one has been considered as the best treatment when the tumor has a big presence. It’s also proven useful as a complement to surgical treatment, significantly reducing the incidence of recurrences after resection.
  • Stereotactic radiosurgery: This one consists of focally administering radiation to the tumor. It’s shown better survival and lower recurrence in those patients with injuries. It can also be controlled better, but there isn’t a significant difference in survival rates in those with 2 or 3 lesions.
  • Chemotherapy: Brain metastases are usually quite resistant to chemotherapy. However, the integration of new therapeutic alternatives, such as target agents and inhibitors of immune control points, has intensified research in this area.

Conclusion

Brain metastases constitute about 90% of the total cases of brain cancer. So, it’s essential to establish a diagnosis as early as possible in order to try to stop the progression of the disease.

There are currently many different treatments and their prognosis continuously improves. However, brain metastasis is a very aggressive cancer and there’s still much to investigate in this area.

Thanks for reading.

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  • Massot-Punyet, R., Almajano, J., & Camacho, J. M. (2000). Metástasis cerebrales. In Revista de Neurologia.
  • Marín, A., Renner, A., Itriago, L., & Álvarez, M. (2017). METÁSTASIS CEREBRALES: UNA MIRADA BIOLÓGICA Y CLÍNICA. Revista Médica Clínica Las Condes. https://doi.org/10.1016/j.rmclc.2017.05.010