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Case Reports

Abstract

A 34-year-old woman presented with a tender, slowly enlarging plaque on the right lateral breast, first noticed 20 years earlier.  Imaging classified the lesion as BI-RADS 3 (probably benign), and core biopsy showed benign breast parenchyma with fibrosis and adenosis. 

 Dermatologic evaluation was pursued due to progressive pain, pruritus, and discoloration. Examination revealed a poorly defined orange-brown plaque with ecchymosis and telangiectasias. The differential diagnosis included fat herniation, morphea, anetoderma, atrophoderma, panniculitis, or cutaneous metastasis of breast cancer. Punch biopsy demonstrated a markedly atrophic dermis infiltrated by a spindle cell proliferation, with minimal atypia and rare mitoses, that infiltrated the subcutaneous septa instead of “honeycombing” the fat. Immunohistochemistry for CD34 was diffusely positive and S-100 protein, epithelial membrane antigen (EMA), and pancytokeratin were negative in the spindle cells. Fluorescence in situ hybridization (FISH) was positive for a COL1A1::PDGFB fusion. Together, these findings supported atrophic dermatofibrosarcoma protuberans (DFSP). The tumor was excised by Mohs micrographic surgery with clear margins. No fibrosarcomatous transformation was seen, and the patient remains recurrence-free. 

Atrophic DFSP is a rare variant that may lack a protuberant component, instead presenting as a flat, indurated, or depressed plaque.  Clinically, this morphology overlaps with benign atrophic processes, increasing the risk of delayed or missed diagnosis. Histologically, the tumor infiltrated along the subcutaneous septa rather than showing the typical “honeycombing” of fat, which may correlate with its clinical appearance lacking a nodular component. Recognition of this variant is essential to avoid misdiagnosis, particularly in long-standing indolent lesions that later progress.