CD34+ Pigmented Fibrous Proliferations: The Morphologic Overlap Between Pigmented Dermatofibromas and Bednar Tumors

Abstract

Pigmented dermatofibrosarcoma protuberans (DFSP; Bednar tumor) constitutes 5%-10% of all cases of DFSP and shows morphologic features that overlap with melanocytic and fibrous proliferations. We report 2 unusual cases of pigmented fibrous proliferations that demonstrate features of dermatofibromas and DFSP. The first case is that of a 19-year-old man with a 3-year history of a slowly growing pigmented lesion on the right arm. On clinical exam, the lesion was a 7-mm firm pigmented papulonodular lesion. The second case is that of a 31-year-old woman with a 4- to 5-year history of a slowly enlarging, asymptomatic "dark area" on the right buttock. On clinical exam, the lesion was a 2-cm darkly pigmented flat nodule. Morphologically, both lesions are primarily dermal proliferations of spindled cells admixed with pigmented dendritic melanocytes. The lesional cells trap collagen fibers at the periphery and there is basal cell hyperpigmentation. Adnexal structures are effaced, but significant trapping of subcutaneous fat is not present. By immunohistochemistry, both lesions show focal CD34 positivity but are negative for Factor XIIIa and melanocytic markers. Although overlap between standard dermatofibromas and DFSP is well documented in the literature, pigmented fibrous lesions with features of both entities are not well described.

Collagen triple helix repeat containing-1 in the differential diagnosis of dermatofibrosarcoma protuberans and dermatofibroma

“…The observation of the frequent expression of stem cell markers such as nestin in DFSP may indicate that it, as well as Bednar tumours, are thus derived from putative, multipotent neuromesenchymal cells; Bednar tumours are composed of melanocytic and neuromesenchymal elements whereas DFSP is a purely neuromesenchymal neoplasm. 24,32,33 It is possible that DFSP may frequently contain multipotent stem cells. Cthrc1 also regulates stem cell differentiation through the Wnt-related signalling pathway.…”

Non‐melanocytic mimics of melanocytic neoplasms

“…Mesenchymal lesions, including scars as well as fibrohistiocytic and vascular tumours, may on occasion be difficult to tell apart from melanocytic lesions ( Table 4). [43][44][45][46][47][48][49][50][51][52][53][54][55] fibrohistiocytic Scars, especially those that are obtained from an area in which Monsel's solution was used previously for haemostasis, can be confused with melanocytic lesions, including melanoma, 43 as they show a proliferation of spindle cells with abundant pigment (Figure 13). However, the clinical history, along with Perls' stain, separates these two entities easily.…”

“…However, the clinical history, along with Perls' stain, separates these two entities easily. It is best to avoid Bednar's tumour 49,50 B. Vascular Epithelioid angiosarcoma 51,52 Perivascular epithelioid cell (PEComa) [53][54][55] Non-melanocytic mimics of melanocytic neoplasms 721 the use of Monsel's solution in biopsies suspected of being melanocytic lesions. Similarly, following excision of melanocytic lesions, especially desmoplastic melanomas, the ensuing scars may be interpreted as containing residual melanocytic cells because some immunohisto-logical markers such as S-100 and P-75 may be expressed in both.…”

“…Recently, McAllister et al 50 reported two cases of a pigmented fibrohistiocytic proliferation of spindle cells admixed with melanocytes, overlying lentiginous melanocyte hyperplasia and collagen trapping but without involvement of the subcutis. Focal but strong CD34 positivity was present in both cases.…”

Blahoslav Bednar (1916-1998) and the tumor which bears his name

“…It is thought to represent the colonization of DFSP by melanocytes [2]. It constitutes 5%-10% of all cases of DFSP and shows morphologic features that overlap with melanocytic and fibrous proliferations [2][3][4][5][6]. There is one report each of a recurrent DFSP transforming into a Bednar tumor, Bednar tumor with prominent meningothelial-like whorls [4], Bednar tumor with dermal melancytosis, and congenital Bednar tumor in a patient with Fanconi anemia [6].…”