Dermatofibroma (fibrous histiocytoma) and variants
Dermatofibroma (fibrous histiocytoma) is a common benign papular or nodular skin lesion composed of variable combinations of fibroblastic cells, macrophages, and coarse collagen.
Dermatofibroma (fibrous histiocytoma) 8832/0
Benign fibrous histiocytoma; histiocytoma (cutis); fibroma durum; subepidermal nodular fibrosis orsclerosis; sclerosing haemangioma.
Dermatofibroma can arise at any age, but is most common in the third and fourth decades of life. The classic type is more common in younger females, particularly on the legs. Other variants have a more equal sex distribution.
It has been debated whether dermatofibroma is inflammatory or neoplastic. Some lesions have shown clonality and recurrent translocations suggesting neoplasia. This entity has also been reported to arise after trauma, insect bites, or folliculitis, suggesting an inflammatory origin. More recently, gene fusions involving PRKC Band PRKCD (encoding protein kinase Cisoforms) have been noted in a subset of cases, confirming a neoplastic nature.
The lesions are most commonly seen on the legs, followed by the arms and trunk. Occasional lesions are seen on the hands, feet, and head and neck. The cellular variant is the subtype most commonly involving the head and neck.
Most dermatofibromas asymptomatic papules are that isolated evolve rapidly and then stabilize. Early stage lesions are typically erythematous, but older ones are brown or skin-toned, often with a peripheral brown rim. The lesions are typically 1 cm in diameter but are occasionally up to 10 cm. They are typically firm, well circumscribed, and symmetrical. Most lesions are raised and dome-shaped and show a central dimple when squeezed. They may be cystic, eroded, or crusted. Occasionally several lesions are present, and rarely there can be dozens, either widely distributed or agminated. Multiple lesions may have no clinical significance, but they have been reported in conditions associated with immunosuppression and in association with immunosuppressive drugs.
There is evidence of fibroblastic, myofibroblastic, and/or macrophage differentiation.
Prognosis and predictive factors
Dermatofibroma is a benign lesion. Incomplete excision may result in local non-destructive recurrence. There is conflicting evidence as to whether dermatofibroma of the face behaves more aggressively than dermatofibroma at other anatomical sites. The risk of local recurrence is higher with the cellular, atypical, and aneurysmal sub-types. Extraordinarily rare lesions have metastasized to lymph nodes and/or lung; most have been of the cellular, atypical, or aneurysmal subtype. There is some evidence suggesting that metastasizing tumours have more chromosomal aberrations than are typical of standard indolent dermatofibroma.
WHO classification of skin tumours, 4th edition (2018): 310-312.