Abstract:

Fibroblastic connective tissue nevi (FCTN) represent a novel and exceedingly rare classification of a benign dermal tumor. Since its initial description in 2012 by de Feraudy and Fletcher, there have only been 52 cases reported in the literature with over 80% demonstrating CD34 positivity. The histologic differential for CD34 positive, mesenchymal tumors has expanded in the past few decades and includes “plaque-like CD34-positive dermal fibroma”, nuchal fibroma, dermatofibrosarcoma protuberans (DFSP), solitary fibrous tumor, desmoplastic fibroblastoma, spindle cell lipoma, dermatomyofibroma and FCTN. Given the clinical management of these individual diagnoses may vary significantly, careful histologic diagnosis by a dermatopathologist is crucial. We present a case of a 34-year-old woman presenting to the dermatology clinic with a two-year history of a 3.3cm firm, asymptomatic bump on her thigh. Initial biopsy demonstrated a paucicellular CD34-positive, factor XIIIa negative spindle cell proliferation concerning for DFSP. However, FISH analysis failed to identify a Col1a1-PDGFB translocation. Conservative excision was pursued, and subsequent tissue sent for expert review resulting in a diagnosis of FCTN. Misdiagnosis of FCTN as DFSP can result in unnecessary invasive procedures and increased morbidity for patients. Here we review the histologic features distinguishing FCTN from other CD34-positive neoplasms to increase awareness about an uncommon diagnosis.

Financial Disclosure:
No current or relevant financial relationships exist.

Brett Keeling

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(Poster #223) Expanding the CD34 differential: A Case of Fibroblastic Connective Tissue Nevus