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Glossary Blog, April 2018: Brain Tumor vs. Brain Cancer

Published on April 30, 2018 in Brain Tumor Information

Our first two monthly Glossary Blogs this year tackled “meaty” topics, CAR T-cell Therapy and Tumor Sequencing.

This month, we wanted to “step-back” and tackle a question that had been brought to our attention, that seemed to be, perhaps, the most basic and fundamental term/concept for this community: Is a brain tumor, brain cancer? Or, are brain tumors cancerous?

Simple enough, right? A simple “Yes” or “No” answer should do, right?

Well, not exactly. Which has caused some confusion and debate in the community.

Let’s take a deeper look.


First, some definitions…

  • Malignancy/Malignant – Tending to be severe and become progressively worse, or (in regard to a tumor), having the properties of a malignancy that can invade and destroy nearby tissue and that may spread (metastasize) to other parts of the body.
  • Metastasize/Metastases/Metastatic – Having to do with metastasis, which is the spread of cancer from the primary site (the place where it started) to other places in the body.

Quick Brain Tumor Overview

A brain tumor is an abnormal growth of cells that form a mass in the tissue of the brain.

Tumors that start and develop directly in the brain or spinal cord are called primary brain or CNS tumors. A tumor that starts in another part of the body and spreads to the brain is called a “metastatic,” or “secondary,” brain tumor (also often called brain metastases and sometimes just “brain mets”).

*For the purpose of the remainder of this discussion, we’ll be focusing on primary brain tumors.

Benign vs. Malignant Tumors

Brain tumors can be classified as either “benign” (non-malignant/non-cancerous) or “malignant.” Malignant is a term that typically implies, and refers to, cancer. And, in fact, the term often has become a stand-in for “cancer.” The terms are often used interchangeably.

Both benign and malignant tumors disrupt normal brain function, cause signs and symptoms, and typically require treatment of some sort.

The biggest difference between “benign” and “malignant” tumors is that malignant tumor cells are much more aggressive and have more of an ability to grow rapidly and spread into otherwise healthy brain and spinal tissue. Benign tumors typically have “well-defined” or clear borders, which means they are well-contained or encased, while malignant tumors typically invade and comingle with healthy tissue and cells. (More on each below).

Now, here is where the question above, and some more confusion, comes into play…

Because of the uniqueness of the brain as an organ, and subsequently the uniqueness of tumors arising in the brain (primary brain tumors), brain tumors are somewhat distinct in how they are categorized when it comes to the concepts of “cancer” and “malignancy,” when compared to tumors and cancers of other organs.

With this in mind, let’s apply these terms to brain tumors:

  • Primary brain tumors that are classified as “benign” are not cancerous. However, benign brain tumors can be considered dangerous and/or life-threatening if they are located in areas of the brain that control vital functions like breathing. A benign tumor will not spread to other parts of the body, but that does not mean that it is harmless.
  • Primary brain tumors that are classified as “malignant” are typically considered cancerous, or brain cancer. We emphasize the word “typically,” because not all doctors agree** that primary malignant brain tumors are always necessarily “brain cancer.” This is because, again, they are not known to metastasize, or spread, to other parts of the body outside the Central Nervous System (though there are some reports on cases where this does happen), a typical “hallmark” for what the biomedical field considers “cancer.”

However, while even primary malignant brain tumors rarely spread to other areas of the body, they can, and often do, spread throughout the brain and central nervous system. In other words, though it’s rare to hear of a primary brain tumor metastasizing to a distant organ, they do spread ‘locally’ and invade other healthy tissue in the brain. For this reason, it is the majority opinion (and indeed how the National Cancer Institute states it) that primary malignant brain tumors should be regarded and classified as a type of cancer – brain cancer*.

  • Secondary (metastatic) brain tumors are always considered cancerous, because they began as a cancer somewhere else in the body and spread to the brain.


So, the short answer to our original question is, “It depends.”

But, for all intents and purposes, and all technicalities aside, the easy way to look at it is like this:

Benign brain tumors are NOT cancerous. Primary malignant brain tumors and secondary brain tumors ARE cancerous. Thus, while not all brain tumors are cancerous, all brain cancers are brain tumors.

More Brain Tumor Basics

  • Even among primary brain and CNS tumors, there are many different types – somewhere around 130-140 different tumor types and subtypes. They form in different cell types, tissues, and different areas of the brain and spinal cord.
  • Brain tumors can occur in both adults and children. The types of tumors that form, and the way they are treated, can be different for children and adults.
  • Metastatic brain tumors most often originate from cancers of the skin (melanoma), breast, lung, kidney, and colon, though virtually any cancer has the ability to metastasize to the brain.
  • Benign Brain Tumors – Benign tumors are typically slow-growing and rarely spread to other areas of the body.  They often have well-defined borders, so surgical removal can be an effective treatment. However, that does not mean these tumors are harmless; the location of a benign brain tumor can have a significant impact on treatment options and be as serious and life-threatening as a malignant tumor. Indeed, traditionally benign brain tumors can sometimes even be considered malignant if they are located in areas of the brain that control vital functions like breathing and heart rate, as they can still grow and put pressure on tissue in the brain. This pressure can cause damage to healthy brain tissue and interrupt normal functions of the brain.
  • Malignant Brain Tumors – Unlike benign tumors, the cell structure of a “malignant” brain tumor is significantly different than that of “normal” brain cells. Malignant tumors tend to grow faster, in a more abnormal way, and are more invasive than benign tumors. Malignant tumors are life-threatening. Sometimes malignant brain tumors are referred to as “brain cancer,” though they do not share all of the characteristics of cancer. Most notably, cancer is characterized by the ability to spread from one organ to another.  It is very rare for a primary brain tumor to spread beyond the brain or spine.

More on brain tumor basics:

Reference/Further Reading

**Some doctors may simply also be choosing not to use the word “cancer,” in referring to primary malignant brain tumors because they wish to distinguish for the patient that their tumor is not a metastasis arising from systemic cancer.

*Note: Classification of primary malignant brain tumors can get even murkier when these tumors are further categorized by grade. For example, all “high-grade” malignant brain tumors (Grade III and Grade IV tumors) meet the criteria for cancer, in that they are aggressive and virtually always spread into other areas of the brain from their main, original site. However, “low-grade” malignant brain tumors (Grade II tumors) are not benign, but they are often slow growing and their potential to reoccur after treatment and/or spread to different parts of the brain can often take decades. In such cases, some clinicians may prefer to not use the term “cancer,” given the significantly less aggressive trajectory of these tumors compared to the Grade III and Grade IV tumors (though, they also typically meet most doctor’s criteria for “cancer.”)

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