From the Guidelines
Dermatofibroma and Merkel cell carcinoma do not have significant histological similarities and are generally not easily confused with each other. When considering the diagnosis of dermatofibroma, it is crucial to differentiate it from other soft tissue neoplasms due to the potential for misdiagnosis, with rates as high as 30%–40% in initial work-ups 1. The key characteristics of dermatofibroma include a storiform pattern of spindle-shaped fibroblasts, collagen deposition, and often hemosiderin pigment, which are distinct from the features of Merkel cell carcinoma, a rare, aggressive neuroendocrine skin cancer with small round blue cells expressing neuroendocrine markers. Some of the challenges in diagnosis can be mitigated by the use of immunohistochemistry and mutational analysis, particularly in diagnostically equivocal or uncertain cases, as recommended by expert consensus initiatives 1. Key points to consider in the differentiation include:
- Histopathological features: Dermatofibromas show a storiform pattern, while Merkel cell carcinomas display trabecular or nodular arrangements.
- Immunohistochemical staining: Merkel cells are positive for cytokeratins and neuroendocrine markers, whereas dermatofibromas typically express factor XIIIa. Given the potential for confusion with other soft tissue neoplasms and the importance of accurate diagnosis, it is strongly recommended that dermatofibroma diagnosis be confirmed by an expert soft tissue pathologist, ideally with mutational analysis in uncertain cases 1.
From the Research
Histological Similarities between Dermatofibroma and Merkel Cell Carcinoma
- There is no direct evidence in the provided studies that suggests dermatofibroma has histological similarities to Merkel cell carcinoma 2, 3, 4.
- However, it is noted that Merkel cell carcinoma can have various histopathologic differentiations, including those that demonstrate squamous cell and eccrine carcinoma features, and those that show melanocytic, lymphomatous, sarcomatous, muscular, and atypical fibroxanthoma-like features 2.
- Dermatofibroma, on the other hand, is a common benign fibrohistiocytic tumor that can show a wide variety of clinicopathological variants, making its diagnosis difficult in some cases 5, 6.
Potential for Misinterpretation
- Merkel cell carcinoma can be misdiagnosed due to its atypical histological or aberrant immunohistochemical findings, and its ability to mimic other skin cancers, such as basal cell carcinoma 2.
- Dermatofibroma can also be misdiagnosed due to its variable clinicopathological features, including atypical presentations such as atrophic dermatofibroma and keloidal presentation of dermatofibroma 6.
- However, there is no evidence to suggest that dermatofibroma is commonly misinterpreted as Merkel cell carcinoma or vice versa 2, 3, 4, 5, 6.