Malignant Glomus Tumor (Glomangiosarcoma), from the CureRays guide library.

Malignant glomus tumor is a very rare cancerous form of the usually-benign glomus tumor — a growth of the tiny temperature-regulating structures in the skin — treated primarily with wide surgical removal, with radiation added for high-risk or unresectable cases.

What it is.

A glomus tumor is a small growth that arises from the glomus body, a tiny structure in the skin that helps regulate body temperature by controlling blood flow, often found under the fingernails. The vast majority of glomus tumors are completely benign and simply cause pain or sensitivity. Very rarely, a glomus tumor is malignant — a cancer sometimes called glomangiosarcoma or 'malignant glomus tumor.' These are diagnosed when a glomus tumor shows worrisome features under the microscope: large size, deep location, atypical cells, or a high rate of cell division. Most malignant glomus tumors behave in a borderline fashion and are cured by complete removal, but a minority can spread to distant sites, especially the lungs. Because it is so rare, an experienced pathologist is essential to make the diagnosis and distinguish it from its common benign relative. Note: this is different from the 'glomus tumors' of the head and neck (paragangliomas), which are a separate condition.

How radiation treats it.

Radiation damages the DNA inside cancer cells so they can no longer divide. For malignant glomus tumor, surgery is the main treatment, but radiation is an important partner when the risk of the cancer returning is higher — for large, deep, or high-grade tumors, or when surgical margins are close or positive — because it treats the microscopic cells left behind and lowers the chance of local recurrence. Shaped external-beam radiation concentrates the dose on the tumor bed while sparing surrounding skin, nerves, tendons, and joints, which matters because these tumors often occur on the hand. If the cancer spreads to a small number of spots in the lungs, focused stereotactic radiation (SBRT) can treat those precisely. Radiation is painless during delivery, given over a series of sessions, and external-beam treatment leaves no radioactivity in the body.

The ways we can treat it.

External-beam radiation (IMRT). Shaped beams treat the tumor bed after surgery while sparing surrounding skin, nerves, and — for tumors on the hand — tendons and joints.

Stereotactic body radiation (SBRT). Focused high-dose radiation can treat a small number of lung metastases precisely when the cancer has spread there.

Brachytherapy (selected). In some sarcomas, radioactive sources placed close to the tumor bed deliver a concentrated dose to a small area while sparing nearby tissue.

Questions we hear often.

Aren't glomus tumors usually harmless? Yes — the vast majority of glomus tumors are completely benign and cause only pain or sensitivity, often under a fingernail. A malignant glomus tumor is very rare and is diagnosed only when the tumor shows specific worrisome features under the microscope. An experienced pathologist is essential to tell the two apart.

Is this the same as a 'glomus tumor' in the head or neck? No. The head-and-neck 'glomus tumors' (such as glomus jugulare or glomus tympanicum) are actually paragangliomas — a different condition with its own treatment. The malignant glomus tumor described here is a skin/soft-tissue tumor related to the temperature-regulating glomus body, often in the hand.

Will I need anything beyond surgery? Most malignant glomus tumors are cured by complete wide removal. Radiation is added for larger, deeper, or more aggressive tumors, or when margins are close, to lower the risk of recurrence. Because spread to the lungs can occur, your team will also recommend follow-up chest imaging.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.