A 71-year-old woman presented with a 2-year history of a depression in the right upper trunk (lateral aspect) that had slowly become more pronounced. The lesion remained asymptomatic. Physical examination revealed a 1.5 cm × 0.8 cm reddish-brown, ovoid depression with a violaceous-gray border and a firm, infiltrated texture on palpation (Fig. 1). Ultrasonography showed a focal area of disorganized dermal architecture with ill-defined margins and increased echogenicity in the adjacent subcutaneous fat. Magnetic resonance imaging (MRI) demonstrated focal cutaneous thinning and slight depression. A skin biopsy specimen showed epidermal atrophy and basal-layer hyperpigmentation. The dermis was thinned and diffusely infiltrated by bland, short spindle cells, which extended to the subcutis (Fig. 2). No notable mitotic figures or cytologic atypia were observed. Immunohistochemical staining of tumor cells was negative for S-100 protein (S-100), smooth muscle actin (SMA), desmin, cytokeratin, and activated coagulation factor XIII (factor XIIIa), and diffusely positive for cluster of differentiation 34 (CD34). A diagnosis of atrophic dermatofibrosarcoma protuberans (DFSP) was made. The patient underwent complete excision with Mohs micrographic surgery, and histopathologic examination confirmed clear margins. At 6-month follow-up, there was no evidence of local recurrence or metastasis. Continued surveillance is planned.
Atrophic DFSP is a rare non‑protuberant variant that often poses diagnostic challenges because it mimics benign sclerotic or atrophic skin disorders[
1], such as localized morphea, atrophic scar, anetoderma, and lipoatrophy. However, the firm, infiltrated consistency and the histopathological and immunophenotypic findings usually confirm the diagnosis. Clinically, the depressed appearance may be related to dermal infiltration by tumor cells and stromal alterations. This variant predominantly affects the trunk of young to middle‑aged adults with a female preponderance, but it can occur at any age[
1]. Immunoreactivity for CD34, combined with negativity for S‑100 and other markers, is crucial for distinction[
1,
2]. Complete surgical excision with clear margins is the standard treatment. Compared with wide local excision, Mohs micrographic surgery yields lower local recurrence rates (1.7% vs. 3.7% in comparative studies, and 1.5% vs. 9.4% in noncomparative studies), and should be strongly considered when available[
3].
Atrophic DFSP typically presents as a long-standing, slowly progressive depressed plaque with a firm, infiltrated texture on palpation. This clinical presentation is easily mistaken for benign conditions such as morphea or anetoderma, emphasizing that persistent atrophic lesions warrant a low threshold for skin biopsy.
Despite its bland histopathologic appearance with minimal cytologic atypia and a very low Ki-67 proliferation index, atrophic DFSP remains a locally aggressive malignancy. Complete surgical excision with histopathologically confirmed clear margins, such as with Mohs micrographic surgery, is essential to prevent local recurrence.
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