This article was last reviewed and updated on May 8, 2019
by Glenda Wright, MBBCh and Allison Osmond, MD FRCPC
A dermatofibroma is a common non-cancerous skin tumour.
It that starts from cells normally found below the surface of the skin.
Dermatofibroma can occur in any location on the body where there is skin.
Skin is the largest organ in your body. Normal skin is made up of different layers. The tissue at the very surface of the skin is called the epidermis. The tissue below the epidermis is called the dermis and it contains blood vessels and connective tissue. Below the dermis is a layer of fat called subcutaneous adipose tissue.
Many different types of cells are normally found in the dermis including fibroblasts and histiocytes. Fibroblasts produce the collagen and other substances that make the dermis strong. Histiocytes are a type of immune cell that protect the body from any infections or toxins that enter through the skin.
What is a dermatofibroma?
A dermatofibroma is a very common type of non-cancerous skin tumour. They grow slowly, have a pink to brown colour, and are usually small and painless. Another name for a dermatofibroma is benign fibrous histiocytoma.
Under the microscope, dermatofibromas are made up of long thin cells that pathologists call spindle cells. These spindle cells look very similar to the fibroblasts and histiocytic cells normally found in the dermis. Giant cells, which are histiocytes that have joined together to form one large cell, are also seen.
The border between a dermatofibroma and the surrounding normal skin can be very hard to see. For this reason, it can be hard for your doctor to remove the entire tumour and a small number of tumours may come back (local recurrence) after they are removed.
There are different kinds of dermatofibromas based on how the tumour looks under the microscope. Pathologists call these tumours variants and like classic dermatofibromas, they are all non-cancerous.
Common variants of dermatofibroma include:
Aneurysmal dermatofibroma – These tumours contain large pools of blood when viewed under the microscope.
Epithelioid dermatofibroma – These tumours contain cells that are bigger and look less like fibroblasts.
Cellular dermatofibroma – These tumours contain an increased number of spindle cells and are more likely to come back (local recurrence) after being surgically removed.
Other variants include clear cell, lipidized, palisaded, and myxoid.
How do pathologists make this diagnosis?
The diagnosis of dermatofibroma is usually made after the entire tumour has been surgically removed and sent to a pathologist for microscope examination. Sometimes, your doctor will remove a small piece of the tumour in a procedure called a biopsy before removing the entire tumour.
It can be very challenging for a pathologist to make the diagnosis of dermatofibroma after only examining a small piece of the tumour because there are other types of tumours that can look very similar to dermatofibroma. In this case your pathologist may offer a list of possible diagnoses which includes dermatofibroma. A final diagnosis will be given after the entire tumour is removed and examined.