Section Editor: Allison Osmond MD FRCPC
June 18, 2026
A dermatofibroma, also called a benign fibrous histiocytoma, is a very common, noncancerous (benign) skin tumor. It develops in the dermis, the thick layer of connective tissue just below the skin’s surface, and usually appears as a small, firm bump that may feel hard to the touch. Dermatofibromas are most often found on the arms, legs, and trunk, but they can occur anywhere on the body.
This article explains what a dermatofibroma is, what the findings in your pathology report describe, and why this growth is considered harmless. Dermatofibromas grow slowly, do not turn into cancer, and in most cases need no treatment, although they can sometimes cause cosmetic concern or mild symptoms such as itching or tenderness.
What causes a dermatofibroma?
The exact cause is not always known. Some dermatofibromas appear to develop after a minor skin injury, such as an insect bite or a thorn prick, while others arise without any clear reason. They are thought to be a reactive overgrowth of cells in the dermis rather than a true tumor, and they are more common in adults, especially women.
What are the symptoms of a dermatofibroma?
Most dermatofibromas cause no symptoms and are noticed only because of their appearance or feel. When symptoms do occur, they may include a firm, round bump usually less than 1 cm across, a color ranging from pink to brown, mild tenderness or itching, and a characteristic central dimple that appears when the skin around the bump is pinched (the “dimple sign”). This dimple sign is a helpful clue that a doctor may use to recognize a dermatofibroma.
How is the diagnosis made?
A doctor may suspect a dermatofibroma based on its typical look and feel, but because other skin growths (some benign and some cancerous) can look similar, the diagnosis often requires examining the tissue under the microscope. Sometimes a small biopsy is taken first, but more often the whole growth is excised (removed) and sent to a pathologist. Because the diagnosis can be difficult when only part of the growth is sampled, complete removal helps ensure an accurate result.
Under the microscope, a classic dermatofibroma grows in the dermis and may extend slightly into the underlying fat. It is composed of spindle-shaped cells (long, narrow cells) and other connective tissue cells, mixed with immune cells, including lymphocytes and macrophages (a type of immune cell that clears debris). A hallmark feature is collagen trapping, in which bundles of collagen (the protein that gives skin its strength) are caught at the edges of the tumor, sometimes forming rounded “collagen balls.” The cells often grow in a storiform pattern resembling swirls or the spokes of a wheel, and the epidermis above the tumor may thicken. The tumor can also stimulate nearby hair follicles, oil glands, or pigment cells, and older dermatofibromas tend to develop more scar-like tissue and fewer cells.
When the appearance is not straightforward, the pathologist may use special stains (immunohistochemistry) to tell a dermatofibroma apart from a low-grade skin cancer called dermatofibrosarcoma protuberans (DFSP), which can look similar. A dermatofibroma is typically negative for the marker CD34 and positive for Factor XIIIa, the opposite of the pattern usually seen in DFSP.
What are the subtypes of dermatofibroma?
Pathologists recognize several subtypes of dermatofibroma based on how the cells look under the microscope. All of them are benign, but some can look unusual or resemble other tumors:
- Cellular dermatofibroma — Made up of tightly packed spindle-shaped cells growing in bundles. It often extends deeper into the fat and may contain small areas of cell death, which is not a sign of cancer.
- Aneurysmal dermatofibroma — Contains blood-filled spaces and a pigment called hemosiderin left behind when blood breaks down, which can make it look like a blood vessel tumor.
- Atypical dermatofibroma — Contains some cells that look unusual in size or shape (pleomorphic cells), and sometimes unusual patterns of cell division, but it is still benign.
- Deep fibrous histiocytoma — A rare subtype found entirely in deeper tissues such as fat or soft tissue, usually with well-defined borders and a swirling storiform pattern.
Can a dermatofibroma turn into cancer?
No. Dermatofibromas are benign and do not become cancerous over time. If a dermatofibroma is not completely removed, it can grow back. A few subtypes, such as cellular and atypical dermatofibroma, can grow larger and are somewhat more likely to return after removal, but even these remain benign and do not spread to other parts of the body.
What happens after this diagnosis?
Most dermatofibromas need no further treatment once diagnosed and can simply be left alone. A dermatofibroma may be removed if it causes discomfort such as pain, tenderness, or itching, if it interferes with daily activities, if it is cosmetically bothersome, or if it cannot be confidently distinguished from another type of growth without removal. When a dermatofibroma is removed, it rarely comes back unless part of it was left behind. Your doctor can advise whether removal or simple monitoring is the better choice for your situation.
What is the prognosis?
The outlook for dermatofibroma is excellent. All forms are benign, meaning they do not spread to other parts of the body or become cancerous. Classic dermatofibromas usually stay stable or slowly shrink over time. The cellular, aneurysmal, atypical, and deep subtypes may grow larger or come back locally if not completely removed, but even these do not metastasize (spread).
Questions to ask your doctor
- Was my growth a typical dermatofibroma, or one of the subtypes?
- Was the entire tumor removed?
- Do I need the whole tumor removed, or can it be safely monitored?
- If it is removed, what are the chances it will grow back?
- Were any special stains needed to tell it apart from other tumors?
- Is there any chance this could be something other than a dermatofibroma?
- What should I watch for after removal?
- Should any of my other skin bumps be checked?
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