Glomus Tumor: Understanding Your Pathology Report

Section Editor: Bibianna Purgina MD FRCPC
September 25, 2026

A glomus tumor is a noncancerous tumor made of cells from the glomus body. The glomus body is a small structure wrapped around tiny blood vessels that helps control blood flow and body temperature. These structures are especially numerous in the fingers and toes.

Most glomus tumors are small, and many are found under a fingernail. They are best known for causing pain that is out of proportion to their size. Removing the tumor usually relieves the pain completely.

A glomus tumor does not spread to other parts of the body. Rare tumors behave like cancer, and pathologists look for specific features to identify those.

This article explains how a glomus tumor is diagnosed and what the type, size, and other findings in your pathology report mean.

A note on names: glomus tumor and paraganglioma

Some head and neck tumors are called glomus jugulare, glomus tympanicum, or glomus caroticum. Despite the shared word, these are not glomus tumors. They are paragangliomas, a different kind of tumor that arises from nerve-related tissue.

If your report says glomus tumor without one of those extra words, this article is for you.

Where do glomus tumors develop?

Most glomus tumors develop in the skin of the hands and feet, and the single most common location is under a fingernail. Others develop in deeper soft tissue, the digestive tract (especially the stomach), or the urinary and reproductive organs.

Tumors under the nail are more common in women. Glomus tumors elsewhere affect men and women about equally, most often in young and middle-aged adults.

What are the symptoms of a glomus tumor?

A glomus tumor in the skin typically causes three symptoms together:

Pain. Often severe, and out of proportion to the size of the lump. It may be constant or come in episodes.
Cold sensitivity. Cold water or cold air triggers or worsens the pain.
Pinpoint tenderness. Pressing one exact spot reproduces the pain, while the surrounding area feels normal.

A tumor under the nail may be visible as a small blue or reddish spot through the nail, and the nail may become ridged or split. Because the lump is often too small to see, these tumors are frequently mistaken for other causes of finger pain for years before the diagnosis is made.

Deep tumors and tumors in an internal organ often cause no symptoms until they are large enough to press on surrounding tissue.

What causes a glomus tumor?

Most glomus tumors occur on their own, without any inherited condition. More than half have a genetic change involving a gene in the NOTCH family. Doctors do not know why these changes occur, and they develop in the tumor cells during a person’s lifetime.

Some people develop several glomus tumors as part of an inherited condition:

Familial glomuvenous malformations. This condition is caused by a change in a gene called GLMN and causes multiple bluish lumps, often present from childhood. Each child of an affected parent has a 50% chance of inheriting the change.
Neurofibromatosis type 1. People with this condition develop glomus tumors of the fingers more often than others do, sometimes in more than one digit.

How is the diagnosis made?

The diagnosis is made after the tumor is removed and examined under the microscope by a pathologist. Imaging such as ultrasound or MRI may be used first to locate a small tumor, particularly under a nail.

Under the microscope, a glomus tumor is made of small, round, pale pink cells with centrally placed nuclei and sharply defined borders. The cells look uniform, meaning they closely resemble one another, and they are arranged in nests around small blood vessels. Mitotic figures, which are cells in the process of dividing, are rare.

What are the types of glomus tumor?

Your report may name a type based on the proportion of tumor cells, blood vessels, and muscle tissue. All are noncancerous:

Solid glomus tumor. The most common type, made mostly of tumor cells with only small vessels between them.
Glomangioma. Contains prominent widened blood vessels surrounded by tumor cells. This type is most often seen when several tumors run in a family.
Glomangiomyoma. Contains tumor cells that blend into surrounding smooth muscle cells.
Symplastic glomus tumor. Contains scattered large, dark, odd-looking nuclei but none of the other worrisome features. This appearance is degenerative, and the tumor is noncancerous.

Immunohistochemistry

Immunohistochemistry uses antibodies to show which proteins cells make. For a glomus tumor, it confirms that the cells match those found in a normal glomus body.

SMA, h-caldesmon, and calponin. These muscle-related proteins are positive in a glomus tumor.
Collagen IV. This protein outlines each tumor cell, producing a pattern that supports the diagnosis.
Desmin, keratins, and S100. These are negative. They help rule out muscle tumors, epithelial tumors, and nerve sheath tumors.

How do pathologists tell benign from malignant?

Almost all glomus tumors are noncancerous. A very small number behave like a cancer, and pathologists use specific features to identify them.

A tumor is reported as malignant when it shows any one of the following:

Deep location and size. The tumor sits deep in the body and is larger than 2 cm.
Abnormal dividing cells. The tumor contains atypical mitotic figures, which are cells dividing in an abnormal way.
Abnormal cells with many divisions. The tumor cells look clearly abnormal, and many of them are dividing.

A tumor may have one worrisome feature without meeting these requirements, such as large size alone. It is then called a glomus tumor of uncertain malignant potential. This means the tumor is very unlikely to behave like cancer, but it warrants follow-up rather than dismissal.

Margins

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

For a noncancerous glomus tumor, a positive margin does not carry the meaning it does for cancer. It does matter for symptoms, because tumor left behind is the usual reason pain returns after surgery. Tumors under a nail are the hardest to remove completely because of the small space involved.

What is the prognosis?

The outlook is excellent. A glomus tumor is noncancerous, does not spread, and removal usually relieves the pain right away.

Pain that returns weeks or months later usually means a small amount of tumor remained, and further surgery normally resolves it. Pain that returns years later may represent a new tumor, particularly in someone who develops several.

A malignant glomus tumor is rare and is managed differently, with wider surgery and imaging to check for spread. Your team will tell you clearly if your report describes this.

What happens after the diagnosis?

Surgery. Removing the tumor is the usual treatment and is curative for most people. For a tumor under the nail, the surgeon lifts or removes part of the nail to reach it, and the nail regrows over several months.
No further treatment. A noncancerous glomus tumor that has been completely removed needs no additional therapy and no routine imaging.
Assessment for an inherited condition. Consider this when several tumors are present, when they appeared in childhood, or when other family members are affected.
Follow-up. Follow-up is recommended for a tumor reported as malignant or of uncertain malignant potential.

Questions to ask your doctor

Was the whole tumor removed, and were the margins negative?
Does my report describe the tumor as benign, of uncertain malignant potential, or malignant?
Which type of glomus tumor was it?
Should my pain settle completely, and how soon?
What should I do if the pain comes back?
If my nail was affected, how long until it grows back normally?
Do I have more than one tumor, and should I be assessed for an inherited condition?