A Large Multinodular Mass on the Back.

A 47-year-old lady presented for evaluation of a progressively enlarging lesion on the back. She described the lesion as an asymptomatic “cyst” that she first noticed 2 years ago. However, over the past year the lesion enlarged and became tender. Physical examination revealed a 5.0 × 4.5 cm hyperkeratotic, indurated brown plaque on the right upper back [Figure 1a]. Dermoscopy demonstrated polymorphic features of multiple colors, milia-like cysts, fissures, and structureless white-to-pink scar like areas [Figure 1b]. An excisional biopsy was performed for histopathological analysis.

Figure 1

(a) A large hyperkeratotic, indurated brown plaque on the patient's right upper back. (b) Dermoscopy illustrating multiple colors, milia-like cysts, fissures, and amorphous white-to-pink scar like areas

Histological findings demonstrated a fibrohistiocytic neoplasm composed of plump histiocytes, slender fibrocytes, and rare multinucleate cells [Figure 2a]. The overlying epidermis demonstrated reactive basaloid hyperplasia and follicular induction [Figure 2b]. The stroma was sclerotic with peripheral keloidal collagen trapping and lymphoplasmacytic aggregates [Figure 2c]. CD34 was negative in the neoplastic cells [Figure 3]. Ki-67 proliferation index was between 5% and 10%. S-100, smooth muscle actin (SMA), and AE1/AE3 immunostains were nonreactive in the neoplastic spindle cells, while Factor XIIIa was positive.

Figure 2

(a) Excisional biopsy specimen revealed a fibrohistiocytic neoplasm composed of plump histiocytes, slender fibrocytes, and rare multinucleate cells (H and E, ×40). (b) The overlying epidermis demonstrated reactive basaloid hyperplasia and follicular induction (H and E, ×100). (c) The stroma was sclerotic with peripheral keloidal collagen trapping and lymphoplasmacytic aggregates (H and E, ×200)

Figure 3

Immunostaining for CD34 demonstrated positivity at the periphery but negative in the neoplastic cells (×20)

What is your diagnosis?

Diagnosis

Giant Cellular Dermatofibroma

Discussion

Dermatofibroma (DF), also known as benign fibrous histiocytoma, represents a benign dermal proliferation of fibroblasts and is the most prevalent cutaneous spindle cell neoplasm. The exact etiology is unknown, but it is typically thought to occur as a result of trauma. A number of clinical and histologic variants of DFs have been described in the literature, including cellular dermatofibroma (CDF), which was first described by Calonje et al. in 1994.[1] CDFs are thought to account for approximately 5% of cutaneous DFs. Like common DFs, these lesions tend to occur on the extremities of young to middle-aged adults but tend to be larger in size. Up to 25% occur on the head and neck. CDFs are typically less than 2 cm in diameter; however, occasionally they can present as a giant dermatofibroma (GDF) as in the patient presented here. The term GDF was first defined by Requena et al. in 1994 to describe a DF that is greater than or equal to 5 cm in diameter, pedunculated, display benign biological behavior despite its size, and shows similar histological characteristics as conventional DF.[2]

The histopathologic findings of CDF are typified by a dermal fibroblastic proliferation with increased cellularity in comparison to common DF.[3] The spindle cell proliferation may encroach the subcutaneous adipose tissue but will not display the same “honeycomb” pattern of infiltration observed in dermatofibrosarcoma protuberans (DFSP). Differentiation of CDF from DFSP is also aided by immunohistochemical evaluation for CD34 and Ki-67 expression. In CDF, weak CD34 positivity limited to periphery of the neoplasm is common, whereas in DFSP the CD34 positivity is strong and diffuse in neoplastic cells. For Ki-67, the proliferation index is increased as observed in our case; in DFSP, the proliferation index is less than 5%. Basaloid hyperplasia (sometimes simulating superficial basal cell carcinoma), follicular induction, and polymorphous inflammation including peripheral lymphoplasmacytic aggregates are helpful ancillary histologic findings in DF.

The differential diagnosis of CDF include atypical fibrous histiocytoma (AFH) and nodular fasciitis.[3] AFH (previously termed “dermatofibroma with monster cells”) is a DF with large, atypical and sometimes bizarre nuclei.[4] In contrast to DF, atypical mitoses are frequently identified in AFH. AFH may display more aggressive behavior including recurrence and, like DFSP, is classified as an intermediate-grade fibrohistiocytic neoplasm. In nodular fasciitis, there is a “tissue culture” appearance to the proliferating myofibroblasts with elongated cytoplasmic processes within a heavily myxoid stroma, features not observed in CDF.[3] This entity is typified by diffuse SMA positivity and a unique translocation involving the USP6 and MYH9 loci.

Although benign, CDFs have reported recurrence rates up to 25%. Unusual DF variants, including CDF, aneurysmal DF, and AFH, are associated with more aggressive behavior, especially when located in unusual sites, such as the head, neck, or digits. For DFs with unusual clinicopathologic findings, there are rare reports of metastases.[56] In these specific contexts, conservative but complete excision is often recommended, but there is no evidence to support routine surgical management of DFs.

Learning Points

DF represents a benign dermal proliferation of fibroblast and it is the most prevalent cutaneous spindle cell neoplasm

CDF is thought to account for approximately 5% of cutaneous DFs

CDF are typically less than 2 cm in diameter but can rarely present as a giant DF

Immunostaining can be useful in distinguishing DFs (CD34 negative, Factro XIIIa positive) from DFSP (CD34 positive, Factro XIIIa negative)

Although benign, CDFs have reported recurrence rates up to 25% with rare reports of metastasis.

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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.