What is the significance of CD10 positivity with minimal Smooth Muscle Actin (SMA) expression in a dermatofibroma?

From the Guidelines

In a dermatofibroma, the finding of CD10 positivity with little smooth muscle actin (SMA) expression is consistent with a diagnosis of dermatofibroma with fibroblastic differentiation. This immunohistochemical profile helps distinguish it from other spindle cell lesions. Dermatofibromas typically show variable CD10 expression in the spindle cells, while SMA is usually minimal or absent in conventional dermatofibromas. The presence of CD10 with minimal SMA supports the fibroblastic nature of the lesion rather than myofibroblastic differentiation. This immunoprofile, combined with typical histological features such as epidermal hyperplasia, hyperpigmentation of basal layer, and storiform pattern of spindle cells, confirms the benign nature of the lesion. Some key points to consider in the diagnosis and management of dermatofibromas include:

• The distinction from dermatofibrosarcoma protuberans (DFSP), which is typically strongly CD34 positive and CD10 negative 1
• The importance of complete excision for diagnosis and treatment, as dermatofibromas are benign lesions with excellent prognosis
• The role of surgical removal in the management of DFSP, with Mohs surgery recommended when possible, and large tumors may require wide local excision and reconstruction 1 No specific treatment is needed beyond complete excision if the diagnosis is confirmed. It is worth noting that the provided guidelines and studies primarily focus on the management of soft tissue sarcomas, including dermatofibrosarcoma protuberans, rather than benign lesions like dermatofibromas 1. However, the immunohistochemical profile and histological features of the lesion in question are consistent with a diagnosis of dermatofibroma, and the management approach should be tailored accordingly.

From the Research

CD10 and SMA Expression in Dermatofibroma

• CD10 expression is common in dermatofibromas, as well as in atypical fibroxanthoma, with studies showing strong CD10 immunoreactivity in 11 of 11 dermatofibromas 2.
• SMA (smooth muscle actin) expression is also observed in dermatofibromas, with many spindle-shaped cells expressing alpha-smooth-muscle actin 3.
• The combination of CD10 and SMA expression in dermatofibromas can be useful in diagnosis, but it is not specific to this condition and can also be seen in other tumors.

Clinical and Histological Features of Dermatofibromas

• Dermatofibromas are common, benign skin tumors composed of fibroblasts and histiocytes in a collagenous stroma 3.
• Cellular dermatofibromas are a variant of dermatofibromas that can recur and metastasize, with a reported recurrence rate of 26% to 50% 4.
• Histological features of dermatofibromas include a mixture of fibroblastic and histiocytic differentiation, with expression of factor XIIIa and alpha-smooth-muscle actin 3.

Diagnosis and Treatment of Dermatofibromas

• Diagnosis of dermatofibromas is typically made by histopathological examination, with surgical excision being the preferred treatment 5.
• The clinical recurrence rate of cellular dermatofibromas can be influenced by factors such as initial lesion size and margin involvement, with larger lesions and positive margins associated with a greater likelihood of recurrence 4.
• A careful discussion between the provider and patient should be had regarding the risk of local recurrence, especially in cases with positive margins or large initial lesion size 4.