Granular Cell Tumor: Understanding Your Pathology Report

Section Editor: Bibianna Purgina MD FRCPC
September 25, 2026

A granular cell tumor is a noncancerous tumor made of large cells filled with tiny granules. The granules give the cells a pink, grainy appearance under the microscope, which is where the tumor gets its name.

Granular cell tumors develop from Schwann cells, the cells that wrap around and protect nerves. They grow slowly and do not usually spread to other parts of the body. A very small number behave like a cancer, and pathologists look for specific features to identify those.

These tumors can develop almost anywhere. The most common locations are the tongue and mouth, the skin and the tissue just beneath it, and the breast. They also occur in the digestive tract, the voice box, and the airways. Most are diagnosed in adults between 30 and 60 years old, and they are more common in women.

This article explains how a granular cell tumor is diagnosed and what the findings in your pathology report mean.

What are the symptoms of a granular cell tumor?

A granular cell tumor usually appears as a single, firm, painless lump that grows slowly. Most are small, often under 3 cm.

Other symptoms depend on the location. You may notice a tumor in the mouth or on the tongue while eating or during a dental visit. A tumor in the voice box can cause hoarseness, and one in the airway may cause cough or breathing symptoms. A tumor in the breast is often found on imaging.

Some people develop more than one granular cell tumor. Recent testing shows these are separate tumors rather than one tumor that has spread.

What causes a granular cell tumor?

Most granular cell tumors are caused by the loss of a gene called ATP6AP1 or, less often, ATP6AP2. These genes help control the acidity inside small compartments within a cell, which is how the cell breaks down and recycles material.

When one of these genes stops working, that recycling process fails and the material builds up inside the cell. This is what produces the granules that give the tumor its name. Changes in these genes are found in roughly 7 out of 10 granular cell tumors.

These changes happen in the tumor cells during a person’s lifetime. They are not inherited, and a granular cell tumor is not passed on to children.

How is the diagnosis made?

A pathologist diagnoses a granular cell tumor after examining tumor tissue under a microscope. The tissue usually comes from surgery that removes the whole lump. For a larger tumor, a small sample may be taken first in a biopsy.

Under the microscope, the tumor consists of large cells with abundant pink cytoplasm, the body of the cell. The cytoplasm is packed with round granules. The nuclei are small and uniform, and very few cells are dividing.

The tumor usually has an ill-defined edge, and the cells spread out into the surrounding tissue rather than forming a neat border. This growth pattern is seen in most granular cell tumors and is not a sign of cancer.

Immunohistochemistry

Immunohistochemistry is a test that uses antibodies to show which proteins tumor cells make. It is often used to confirm this diagnosis. Your report may include some of the following:

S100 and SOX10. Schwann cells make these proteins, and they are positive in granular cell tumor. They support the origin of this tumor from nerve sheath cells.
CD68. This marker highlights the granules inside the tumor cells and is also positive.
Cytokeratins. These proteins are negative. They are found in epithelial cells, so a negative result helps rule out a carcinoma.

Two findings that can be mistaken for cancer

Granular cell tumors produce two findings that look concerning but are expected for this diagnosis:

Changes in the overlying skin or lining. A granular cell tumor can cause the surface layer above it to thicken and grow downward. Pathologists call this pseudoepitheliomatous hyperplasia. On a small or superficial biopsy, it can closely resemble squamous cell carcinoma, a type of skin and mucosal cancer. Examining the whole tumor usually resolves the question.
Perineural invasion. Tumor cells are sometimes seen around small nerves. For many cancers, this finding matters. In a granular cell tumor, it can occur without meaning the tumor is cancerous, and it does not predict how the tumor will behave.

How do pathologists tell benign from malignant?

Fewer than 2 in 100 granular cell tumors behave like a cancer. Pathologists use a set of six microscopic features to sort them out:

Necrosis. Areas of dead tumor tissue.
Spindling. Tumor cells that become long and thin rather than round.
Nuclear changes. Enlarged nuclei with prominent centers called nucleoli.
Dividing cells. An increased number of cells in the process of dividing.
High nuclear-to-cytoplasmic ratio. The nucleus takes up more of the cell than usual.
Pleomorphism. Tumor cells that vary in size and shape.

The number of features present determines the category:

Benign. None or only one of these features. This describes most granular cell tumors.
Atypical. Two features. These tumors are usually followed more closely, and most still behave in a noncancerous way.
Malignant. Three or more features. This is rare, and these tumors are treated as a cancer.

Margins

A margin is the edge of tissue cut by the surgeon. Because a granular cell tumor has an ill-defined edge, tumor cells can reach a margin even when the lump appeared to be removed completely.

A positive margin raises the chance that the tumor will come back in the same place. For a noncancerous granular cell tumor, your doctor may recommend either further surgery or simply watching the area, depending on the location and how much tumor remains.

What is the prognosis?

The outlook for a noncancerous granular cell tumor is excellent. Complete removal is usually curative, and the tumor does not spread.

Tumors that come back usually do so at the original site, and this is more likely when the tumor reached a margin. A tumor that comes back is still noncancerous.

The rare malignant granular cell tumor behaves differently. It can spread to lymph nodes, lungs, and bone, and it requires wider surgery and closer follow-up. Your team will tell you clearly if your report describes this.

What happens after the diagnosis?

Surgery. Removing the tumor is the usual treatment. The surgeon aims to take a small rim of normal tissue around it, because of the ill-defined edge.
Observation. A small tumor that has been completely removed needs no further treatment. Follow-up is usually limited to watching the area.
Further treatment. Additional surgery may be considered when the tumor reaches a margin, especially in a location where a recurrence would be difficult to manage.
Malignant tumors. A team experienced in sarcomas and related tumors manages these, with wider surgery and imaging to check for spread.

Questions to ask your doctor

Does my report describe a benign, atypical, or malignant granular cell tumor?
Was the whole tumor removed, and were the margins negative?
If the tumor reached a margin, do I need more surgery?
Is there a chance the tumor will come back?
Do I need follow-up appointments or imaging?
My report mentions perineural invasion. What does that mean here?
Should any other lumps I have be checked?