Brain Cancer: How Primary and Metastatic Tumors Differ


There are significant differences among brain tumors, especially with regards to where they originate. The origin of a brain tumor is important because this will likely affect a person’s cancer outcome and the course of treatment prescribed by the doctor.


Differentiating Between “Primary” and “Metastatic” Brain Tumors

The terms primary and metastatic describe where the tumor has originated, and brain tumors are generally classified as one or the other. Primary brain tumors arise from the brain or spinal cord while metastatic brain tumors, also termed secondary brain tumors, arise from other tissue and have spread to the brain. This is the most basic form of classifying brain tumors, but yields great insight into the characteristics of these complex growths, and how they might be treated.

Primary Brain Tumors

Primary brain tumors are those that originate in the brain and spinal cord, which is collectively known as the central nervous system, or CNS. These tumors tend to stay within the CNS, rarely spreading to the rest of the body. Primary brain tumors can develop in children and adults but are considered to be rare in both populations. That being said, primary brain tumors that develop in children and adults differ in the following ways:

  • The tumors usually develop in different parts of the brain
  • The tumors develop from different cells
  • The tumors may require a different treatment and have a different prognosis, or outcome 

Despite their rarity, the incidence of primary brain tumors is increasing. This is partly due to the fact that people now have a higher life expectancy, and doctors are more skilled in diagnosing brain tumors than in the past. This all being said, the causes of primary brain tumors remains to be mainly unknown. Researchers believe that in some cases radiation exposure or gene changes play a role in brain tumor development.

It’s important to understand that there are a number of different types of brain tumors that can develop, and the symptoms vary based on the location of the tumor and its size. In addition, primary brain tumors can be malignant, or cancerous, or benign (noncancerous). 

Metastatic Brain Tumors

Unlike primary brain tumors, metastatic brain tumors originate in another part of the body and spread to the brain. Metastatic brain tumors are actually more common than primary brain tumors. Cancer from another part of the body spreads, or metastasizes, to the brain through the bloodstream or through lymphatic vessels.

While a number of different types of cancer can metastasize to the brain, here are a few common ones:


This cancer can spread anywhere in the body. It first tends to spread to the lymph nodes near where it first started and can then spread to the brain, lungs, liver, and bones or other areas of the skin.

Breast cancer

As this cancer progresses, it may affect any organ, most commonly the liver, lungs, and brain, but also can spread to the bones.

Lung cancer

This cancer can spread to the other lung but also may spread to almost any organ of the body, most often the adrenal glands, liver, bones, or brain.

In some rare cases, a metastatic brain tumor is discovered before the originating cancer site is detected. In these instances, it’s called “metastasis of unknown origin.” Because metastatic brain tumors do not have the same cellular composition as primary brain tumors, a brain biopsy is often how these tumors of unknown origin are diagnosed.

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