Many tumors of the central nervous system stay under control for years with treatment. Indeed, some patients enjoy a full life after diagnosis. We wish we could say that everyone experiences good outcomes, but for some people these tumors cause disability or death.

How well a person fares after being diagnosed with a brain or spinal tumor depends on a number of things, including:

• The type and location of the tumor
• How abnormal the cells that form the tumor look
• How quickly, or aggressively, they grow and spread
• The person’s overall health and level of functioning at the time of diagnosis
• The treatment received

Actually, a person who has a tumor might not have cancer. “Tumor” simply means an abnormal mass of cells. Some tumors contain cancerous cells; others do not.

To understand how tumors and cancer develop, you need to know that many of the cells in our body are constantly growing and splitting to form new ones. One cell becomes two, two change into four, and so on. When cells grow old, they die, and new ones replace them.

All cells contain code that tells them what to do, but sometimes mistakes appear in it. As a result, the abnormal cells may grow and divide wildly, thereby making other unruly cells that do the same. Less often, the cells simply outlive their usefulness. In any case, the cells may then form a tumor. Cancer results when the tumor cells grow so fast that they threaten to harm tissue to which they spread.

Many patients and relatives ask, “Is it benign or malignant?” They hope for “benign,” having heard that benign tumors do less harm than malignant ones. However, the distinction between benign and malignant matters less for tumors that start in the brain or spine than in other body parts.

While both benign and malignant tumors can grow, benign ones stay separate from nearby tissue because a “wrapper” surrounds them. As long as they stay benign, they do not spread to distant sites. Treatment can usually remove them completely.

Even so, in the enclosed spaces of the brain and spinal cord, benign tumors can cause big problems. They can press against the skull, spinal cord, or nerves. They can block the flow of blood or cerebrospinal fluid, which cushions the brain and spinal cord. They can hurt nerves or other tissue. In these ways, so-called “benign” tumors can steal patients’ lives or abilities. Furthermore, they sometimes turn malignant.

Unlike benign tumors, malignant ones lack clear edges and tend to invade deep into nearby tissue. This makes it hard to remove them or even to know whether treatment got rid of every last bit of them. Also, they are more likely than benign tumors to return. In most of the body, malignant tumors often spread far from where they started, but those that arise in the brain or spinal cord rarely go beyond the central nervous system.

More commonly, cancer in other parts of the body spreads to the central nervous system. The spreading process, called “metastasizing,” starts when a cancerous cell breaks off from the original tumor and travels to another spot. There it may make new cells and, with them, grow into a malignant tumor. Cancer otherwise controlled by treatment may even escape to the brain and thrive there, perhaps because most of the usual cancer-fighting drugs cannot enter the brain easily.

“Primary” simply refers to a tumor at its original site. For instance, if imaging shows a tumor in the spine that began there, doctors would call it a “primary spinal tumor.” They would dub any new tumors that might grow from it “secondary” or “metastatic.”

Typically, metastatic cancer in the central nervous system results from wayward cells roaming there from other parts of the body, such as a lung, breast, or kidney. This can cause severe, even deadly, effects on the brain. To help patients live longer and better, doctors tend to aggressively treat tumors that spread to the brain.

Some brain or spinal tumors receive a grade, a shorthand way of saying how likely they are to grow and spread. A doctor called a pathologist gives the grade after studying tissue from the tumor through a microscope. High-grade tumors not only look stranger than lower-grade ones, they act more aggressively.

In contrast to grading, staging describes the actual degree of spreading, based on information from multiple sources. No standard staging method exists for brain or spinal tumors because they rarely spread beyond the central nervous system. However, tumors that have spread to the brain or spine are automatically deemed stage IV cancer.