Neurofibroma: Understanding Your Pathology Report

Section Editor: Bibianna Purgina MD FRCPC
September 25, 2026

A neurofibroma is a noncancerous tumor that develops from the cells surrounding and supporting a nerve. It is the most common noncancerous peripheral nerve sheath tumor.

Unlike a schwannoma, which is made of one cell type and pushes the nerve aside, a neurofibroma contains several cell types and grows among the nerve fibers. Neurofibromas do not spread to other parts of the body.

Most people with a neurofibroma have a single tumor and no related condition. A minority have many neurofibromas as part of an inherited condition called neurofibromatosis type 1.

This article explains how a neurofibroma is diagnosed, what the type and other findings in your pathology report mean, and when a neurofibroma needs closer attention.

What are the types of neurofibroma?

Your report will usually describe the type, which depends on where the tumor is and how it grows:

Cutaneous neurofibroma. This type forms a soft lump in or just under the skin. It is the most common type and what most people mean when they say neurofibroma.
Intraneural neurofibroma. This type grows inside a nerve and makes that part of the nerve look thickened.
Diffuse neurofibroma. This type spreads out through the fat beneath the skin rather than forming a rounded lump. It often appears as a thickened plaque, usually on the head or neck.
Plexiform neurofibroma. This type involves several nerve branches at once and has an irregular, rope-like shape. It is closely associated with neurofibromatosis type 1 and usually begins in early childhood.

The type matters because the risk of a neurofibroma changing into a cancer over time applies mainly to plexiform and other deep tumors. A cutaneous neurofibroma essentially never changes in this way.

What are the symptoms of a neurofibroma?

Most neurofibromas are painless lumps that grow slowly. A cutaneous neurofibroma is soft and may move slightly when you press it.

Tumors on larger, deeper nerves can cause tingling, numbness, pain, or weakness in the area supplied by that nerve. A plexiform neurofibroma can grow large enough to change the shape of a limb or part of the face, and it may cause discomfort or limit movement.

What causes a neurofibroma?

A neurofibroma develops when nerve sheath cells lose the function of a gene called NF1. This gene makes a protein called neurofibromin, which normally acts as a brake on signals that tell cells to grow. When the brake is lost, the cells form a tumor.

In most people, this change happens by chance in the tumor cells during their lifetime. It is not inherited, and a single neurofibroma is not a reason to suspect an inherited condition.

Some people inherit a change in one copy of the NF1 gene, which causes neurofibromatosis type 1. People with this condition develop many neurofibromas over their lifetime, often including plexiform tumors, along with other features such as light brown skin patches called cafe-au-lait spots. If you have several neurofibromas or other features of this condition, your doctor may recommend genetic counseling. Our article on hereditary cancer syndromes explains how inherited gene changes are tested.

How is the diagnosis made?

A pathologist diagnoses a neurofibroma after examining tumor tissue under a microscope. The tissue may come from a biopsy or from surgery that removes the whole tumor.

Under the microscope, a neurofibroma contains a mixture of cell types, including nerve sheath cells, fibroblasts, and immune cells. Most are spindle cells, which are long and thin with wavy, dark nuclei. They sit in a background of collagen and myxoid tissue, which looks light blue under the microscope, and the tumor blends into the surrounding tissue rather than having a capsule.

Very few of the cells are dividing. Mild cytologic atypia, meaning cells that look slightly abnormal, can be seen in an ordinary neurofibroma and is not a sign of cancer on its own.

Immunohistochemistry

Immunohistochemistry is a test that uses antibodies to show which proteins cells make. For a neurofibroma, the pattern reflects the mixture of cell types in the tumor.

S100 and SOX10. These proteins are made by nerve sheath cells. In a neurofibroma, they are positive in some cells but not all, reflecting the mixture. In a schwannoma, nearly every cell is positive.
CD34. This protein is positive in the fibroblasts scattered through the tumor, often in a pattern that reports describe as fingerprint-like.

These stains are not always needed. They are most useful when the tumor is unusual or when another diagnosis needs to be ruled out.

When does a neurofibroma need closer attention?

An ordinary neurofibroma is noncancerous and stays that way. In people with neurofibromatosis type 1, a deep or plexiform neurofibroma can slowly change over years into a cancer called a malignant peripheral nerve sheath tumor. People with this condition have an estimated 8% to 13% lifetime risk.

Pathologists recognize an in-between stage on the way to this change. It is called an atypical neurofibromatous neoplasm of uncertain biologic potential, usually shortened to ANNUBP. This diagnosis is made when a neurofibroma shows more crowded or abnormal cells and some loss of its usual structure, but not enough to be called a cancer.

Certain changes in a known neurofibroma should be reported to your doctor:

Rapid growth. A lump that becomes noticeably larger over weeks or months.
New pain. Pain that persists, especially at night.
New weakness or numbness. A change in how the limb or area works.

Margins

A margin is the edge of tissue cut by the surgeon. Your report may note whether the tumor reaches the cut edge.

Because a neurofibroma grows among the nerve fibers, removing all of it can mean sacrificing part of the nerve. Surgeons often leave a small amount of tumor behind to preserve movement and sensation. A positive margin here does not carry the meaning it does for cancer. It means the lump may slowly come back in that area.

What is the prognosis?

The outlook is excellent for a single neurofibroma. It is noncancerous, does not spread, and removal is usually curative. A tumor may come back slowly if part of it was left behind to protect the nerve.

For people with neurofibromatosis type 1, the outlook depends on the condition as a whole rather than on one tumor. Regular assessment allows doctors to investigate any tumor that starts behaving differently early.

What happens after the diagnosis?

Treatment depends on the type of neurofibroma, its location, and the symptoms it causes.

Observation. Doctors may monitor a small, painless neurofibroma. Many people with cutaneous tumors never need treatment.
Surgery. Removal is considered when a tumor is painful, growing, affecting function, or bothersome in appearance. The surgeon balances complete removal against preserving the nerve.
Medication for plexiform tumors. Medicines called MEK inhibitors can shrink plexiform neurofibromas in some people with neurofibromatosis type 1, particularly when the tumor cannot be removed with surgery. Your specialist can explain whether this applies to you and what is available where you live.
Ongoing care for neurofibromatosis type 1. People with this condition are usually followed in a clinic with experience, which includes monitoring for changes in existing tumors.

Questions to ask your doctor

Which type of neurofibroma does my report describe?
Was the whole tumor removed, or was part left to protect the nerve?
Does my report mention atypical features or ANNUBP?
Is there a chance this tumor could come back?
Should I be assessed for neurofibromatosis type 1?
Do I need follow-up imaging or examinations?
Which changes in a lump should prompt me to call?