Brain Tumors: Types, Causes, Symptoms & Side Effects

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson is about brain tumors, or uncontrolled growth of cells in the brain. We will go over different types of brain cancer, causes, symptoms and side effects of treatment.

Tumors Versus Cancer

Cells are only supposed to grow a certain amount. Think about how we grow during childhood. We eventually stop growing and cell division, or the process of making new cells, slows down. But, what happens if we can't turn on the breaks for cell division? What would happen to our bodies? The answer is tumors.

Tumors are masses of uncontrolled cell growth. The word tumor is usually associated with cancer, but it doesn't always turn into cancer. A tumor just means an area of the body where cells are growing out of control. When a tumor becomes cancerous, it starts to move around the body and invading other tissues. Think of a tumor as an army in reserve, not actively being deployed yet. During cancer, our armies mobilize and invade other countries.

The tumor on the right does not invade other tissues, where as the cancer cells on the left do
tumor vs. cancer

A brain tumor is a mass of uncontrolled cell growth, specifically in the brain. The tumor may be benign, meaning non-invasive, or cancerous, meaning it invades other tissues. Tumors still crowd out other functioning cells in the area, so both are dangerous for the person.

Types of Brain Tumors

There are two main types of brain tumors, and each one is classified based on what kind of cells are dividing out of control.

The first type of brain cancer is gliomas. Gliomas occur when supporting cells in the brain divide out of control. Types of supporting cells include astrocytes, glial cells, and Schwann cells. These cells help the main cells in the brain, the neurons, by providing physical support, nutrients and protecting them.

Glioblastoma in a cross section of the brain

Non-Glioma tumors occur when the actual cells of the brain, neurons, or the cells that make up the layers surrounding the brain, called the meninges, divide out of control. Below is a picture of a meningioma, a tumor of the meninges, the outer layer of the brain.


Certain parts of the brain form tumors more often than others. The cerebellum, pituitary gland and meninges are the most common site of tumors in the brain.

What Causes Brain Tumors?

As we've stated, all tumors are caused by uncontrolled cell growth. There are three main factors that can cause tumors to form, chemicals in the environment, called carcinogens, pathogens, or genetics.

Chemicals in the environment that can cause tumors are called carcinogens. Normally, the cell has a series of signals, similar to traffic lights, that tell it to keep growing and dividing, or to stop. Carcinogens change the cell's DNA, creating mutations, which cause the cell to no longer listen to those stop and go signals. The result is a cell that can't tell when to stop dividing and creates a tumor.

DNA after exposure to a carcinogen
mutations in DNA

Pathogens are bacteria or viruses that can infect our bodies. Sometimes, these pathogens can insert their DNA into the brain cells' DNA. The pathogen's DNA tells the cell to continue dividing despite needing to stop. Notice that pathogens insert their DNA into the brain cells' DNA, whereas chemicals change the DNA sequence.

Genetic mutations can also cause brain tumors. Pathogens or carcinogens can cause mutations to happen, but sometimes people inherit a mutation from a parent or it might occur by accident during normal cellular processes. When cells make more DNA, which is necessary to make new cells, sometimes there are mistakes in copying, which lead to mutations. These mutations are typically in genes that regulate many other genes in the cell, causing the changes in cell division to amplify.

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