Nodular Fasciitis: Understanding Your Pathology Report

Section Editor: Bibianna Purgina MD FRCPC
October 3, 2026

Nodular fasciitis is a noncancerous growth made of fibroblasts and myofibroblasts, the cells that build connective tissue and help wounds heal. It often develops in or near the fascia, a thin sheet of tissue that wraps around muscles.

Nodular fasciitis is known for growing quickly, often over just a few weeks. That rapid growth is alarming, and both patients and doctors sometimes worry about cancer. Nodular fasciitis is not cancer. It does not spread, and it usually stops growing and shrinks on its own.

This article explains how nodular fasciitis is diagnosed, why it can be mistaken for cancer, and what the findings in your pathology report mean.

Who gets nodular fasciitis?

Nodular fasciitis is most common in young adults between 20 and 40, although it can occur at any age, including in children. It affects men and women about equally.

The forearm is the most common site. Other common sites include the upper arm, the trunk, and the head and neck. In children, the head and neck are the most frequent location.

What are the symptoms of nodular fasciitis?

The typical story is a lump that appears and grows over a few weeks. Most are less than 3 cm across when they are removed, and many are around 2 cm.

The lump may be tender or mildly painful. Some people remember a minor injury at the same spot, although most do not.

What causes nodular fasciitis?

Most cases of nodular fasciitis have a change involving a gene called USP6. A piece of one chromosome becomes attached to another, which is called a translocation. This rearrangement switches on the USP6 gene. The most common partner gene is MYH9.

The discovery of this change showed that nodular fasciitis is a true growth rather than simply a reaction to injury. Unlike a cancer, however, it is self-limiting. It grows for a short time and then stops and fades away, which is why pathologists sometimes describe it as a transient tumor.

This change develops only in the growth itself. It is not inherited and cannot be passed on to children.

How is the diagnosis made?

A pathologist makes the diagnosis after examining tissue under a microscope. The tissue may come from a biopsy or from an excision, which removes the whole lump.

Under the microscope, nodular fasciitis is made of plump fibroblasts and myofibroblasts arranged loosely, often in short, curving bundles. Pathologists often describe the pattern as resembling cells grown in a laboratory dish, which they call a tissue culture-like pattern.

The growth contains crowded areas, called hypercellular areas, next to looser areas with fewer cells, called hypocellular areas. The looser areas are often gel-like and described as myxoid. Small amounts of bleeding and scattered immune cells are common.

Why can nodular fasciitis look like a cancer?

Nodular fasciitis has several features that are also seen in sarcomas, which are cancers of connective tissue. It grows quickly, it is densely packed with cells, and many of those cells are dividing.

For this reason, nodular fasciitis has historically been one of the noncancerous growths most often mistaken for a sarcoma. Experienced pathologists recognize the combination of features that sets it apart. The cells look uniform and healthy, the dividing cells divide normally, and the growth has the characteristic loose, tissue culture-like pattern.

On a small biopsy, these features can be hard to see. The sample may show only the most crowded areas. In that case, your pathologist may not be able to give a final diagnosis until the whole lump is removed or extra tests are done.

Immunohistochemistry

Immunohistochemistry is a test that uses antibodies to show which proteins cells make. It helps confirm nodular fasciitis and rule out other growths. Your report may include some of the following:

SMA. This protein is positive, which fits with the myofibroblasts that make up the growth.
Desmin. This muscle protein is usually negative or only weakly positive.
CD34, S100, and cytokeratins. These are negative. They help rule out other tumors that can look similar.

Molecular testing

When the diagnosis is uncertain, the pathologist may test for the USP6 rearrangement. The most common test is fluorescence in situ hybridization (FISH), which uses glowing probes to show whether the USP6 gene has broken apart. Next-generation sequencing (NGS) can also identify the partner gene.

Finding a USP6 rearrangement strongly supports the diagnosis of nodular fasciitis and helps rule out a sarcoma. When nodular fasciitis has its typical appearance, molecular testing is usually not needed.

Margins

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

For nodular fasciitis, a positive margin is not a cause for concern. Because the growth is self-limiting, any small part left behind usually fades away on its own. Further surgery is not needed because of a positive margin alone.

What is the prognosis?

The outlook is excellent. Nodular fasciitis is noncancerous, does not spread, and does not become cancer.

It rarely comes back, even when it was not completely removed. Some lumps resolve after a biopsy alone, without further surgery. Because recurrence is so rare, doctors usually re-examine a lump that does come back to confirm the original diagnosis.

What happens after the diagnosis?

No further treatment. If the lump has been removed, no further treatment is needed. A positive margin does not change this.
Observation. If the diagnosis was made on a biopsy, the remaining lump may be watched, since it often shrinks and disappears on its own.
Follow-up. Routine follow-up is not needed. Your doctor may ask you to return if the lump grows again after removal.

Questions to ask your doctor

Was the whole lump removed, and does it matter if it was not?
Was molecular testing for USP6 done, and was it needed?
Do I need any further treatment?
If the lump was only biopsied, should I expect it to go away on its own?
What should I do if a lump comes back in the same place?