Brain Tumors: Primary - Introduction

Introduction

Brain tumors are composed of cells that exhibit unrestrained growth in the brain.

They can be benign (noncancerous, meaning that they do not spread elsewhere or invade surrounding tissue) or malignant (cancerous).

Cancerous brain tumors are further classified as either primary or secondary tumors.

Primary Brain Tumors

Primary tumors start in the brain, whereas secondary tumors spread to the brain from another site such as the breast or lung. (In this report, the term "brain tumor" will refer mainly to primary malignant tumors, unless otherwise specified.)

---

---

Benign Brain Tumors. Benign tumors represent half of all primary brain tumors. Their cells look relatively normal, grow slowly, and do not spread (metastasize) to other sites in the body or invade brain tissue. Benign tumors can still be serious and even life threatening if they are in vital areas in the brain where they exert pressure on sensitive nerve tissue or if they increase pressure within the brain. While some benign brain tumors may pose a health risk, including risk of disability and death, most are usually successfully treated with techniques such as surgery.

Click the icon to see an image of a primary brain tumor.

Malignant Brain Tumors. A primary malignant brain tumor is one that originates in the brain itself. Although primary brain tumors often shed cancerous cells to other sites in the central nervous system (the brain or spine), they rarely spread to other parts of the body.

Brain tumors are generally named and classified according to either of the following:

• The type of brain cells from which they originate
• The location in which the cancer develops

The biologic diversity of these tumors, however, makes classification difficult.

Secondary (Metastatic) Malignant Brain Tumors

A secondary (metastatic) brain tumor occurs when cancer cells spread to the brain from a primary cancer in another part of the body. Secondary tumors are about three times more common than primary tumors of the brain. Usually, multiple tumors develop. Solitary metastasized brain cancers may occur but are less common. Most often, cancers that spread to the brain to cause secondary brain tumors originate in the lung, breast, kidney, or from melanomas in the skin.

All metastatic brain tumors are malignant. This report discusses primary malignant brain tumors.