Brain Tumor Diagnosis and Brain Cancer Stages and Grades

Nov. 14, 2025

This page was reviewed under our medical and editorial policy by Keng Lam, M.D., assistant clinical professor, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte.

Brain tumors are abnormal growths of cells in or around the brain. Some are cancerous while others are benign, or non-cancerous. Patients who experience symptoms of a brain tumor may undergo tests and scans to check for signs of any unusual masses in the brain.

The diagnosis process can be scary, but the care team is there to answer any questions the patient may have. “The number one question I get is whether or not there's something patients did or inherited that led to the brain tumor diagnosis,” says Keng Lam, M.D., a neuro-oncologist at City of Hope in the Los Angeles area. “In almost all cases, there's nothing they did that led to having a brain tumor.”

How to Test for Brain Tumors

Diagnosing a brain tumor may involve one or more scans, a biopsy or other kinds of tests. For many people, the first steps include an examination by a neurologist – who is a doctor who specializes in the brain and nervous system – or a scan of the brain.

Neurologic Exam

A neurologist or neurosurgeon may conduct a neurologic examination to look for signs of changes to how the brain is working. This may include testing a patient’s reflexes and balance, as well as their vision, hearing and memory.

MRI Scan

Magnetic resonance imaging (MRI) is a type of scan that produces images of the inside of the body. These images can help doctors see the location and size of a tumor. There are also specialized types of MRI that may be used to look for changes to the brain’s biochemistry or blood flow, which may help determine what kind of tumor it is and whether it is fast- or slow-growing.

CT Scan

A computed tomography (CT) scan uses X-rays to create an image of the inside of the body. Though it is less commonly used than an MRI, a CT scan may be recommended if patients have a medical reason that makes an MRI impossible or if doctors want to get more detailed pictures of the bones or tissue surrounding the site of tumor.

How Is Brain Cancer Diagnosed?

If doctors discover a brain tumor, most patients then undergo other testing to determine whether the tumor is cancerous or not.

PET Scan

A positron emission tomography (PET) scan uses imaging technology to create a three-dimensional image of the inside of the body. Before a PET scan, patients are injected with a small amount of radioactive material. This material shows up on the results of the PET scan and can help determine whether a tumor is cancerous or not as well as how fast it may be growing.

Biopsy

A biopsy is a procedure in which a small amount of tissue is removed from a tumor and examined in a lab. A biopsy can reveal vital information about the type of tumor a patient has and whether it is growing quickly or slowly.

• A stereotactic biopsy involves guiding a thin needle to the site of a tumor site and removing a small sample of tissue. It is most often recommended when a tumor is in an especially risky or sensitive area of the brain.
• A surgical biopsy involves removing a part of the skull in a process called a craniotomy, and then removing most or all of a tumor (this may also be called tumor debulking). It is most often used if a patient has a tumor that may benefit from being treated surgically.
• A spinal tap may also be recommended if doctors suspect that a brain tumor may have spread beyond the brain and into the spinal cord. This procedure involves inserting a needle into the lower back to collect a sample of cerebrospinal fluid for examination.

Stages of Brain Cancer

Brain tumors are staged differently to most other cancer types. This is because brain cancer – unlike other kinds of cancer – tends not to spread beyond the central nervous system.

Instead of stages, doctors assign brain tumors a grade between 1 to 4, based on the results of any diagnostic tests or imaging. Lower-grade brain tumors tend to be slower-growing and less likely to spread, while higher-grade brain tumors are faster-growing and more likely to spread.

Grade 1 Brain Tumor

A grade 1 brain tumor is usually slow-growing and less likely to spread. When viewed under a microscope, the cells in a grade 1 brain tumor look more similar to normal cells.

Grade 2 Brain Tumor

The cells in a grade 2 brain tumor look less like normal cells. At grade 2, a brain tumor is usually slow-growing but may spread to nearby parts of the brain.

Grade 3 Brain Tumor

A grade 3 brain tumor is a cancerous type of brain tumor that is faster-growing and may spread to other parts of the brain or spinal cord. The cells in a grade 3 brain tumor look more abnormal. Another term sometimes used for grade 3 brain tumors is “anaplastic tumors.”

Grade 4 Brain Tumor

Grade 4 brain tumors are the fastest-growing type of brain cancer and have cells that look very abnormal. At grade 4, a brain tumor is more likely to spread to other parts of the brain or spinal cord or to come back after treatment.