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Case Reports

Abstract

Pleomorphic fibroma is an uncommon benign cutaneous neoplasm that typically presents as a solitary, asymptomatic papulonodule on the trunk or extremities. Histologically, it is characterized by a hypocellular collagenous stroma containing pleomorphic spindle cells and bizarre, multinucleated giant cells. The presence of adipocytic differentiation, a rare variant, creates a significant diagnostic challenge due to its morphological overlap with malignant entities, particularly pleomorphic liposarcoma.

We present the case of a 53-year-old male with a slowly enlarging, polypoid nodule on his right superolateral back. Microscopic examination revealed atypical cells with smudgy, hyperchromatic nuclei set within a prominent myxoid and mature adipocytic stroma. Critically, both mitotic activity and necrosis were absent. Immunohistochemical analysis showed the neoplastic stromal cells were strongly and diffusely positive for CD34, with focal reactivity for CD68 and factor XIIIa. This staining profile, particularly the diffuse CD34 positivity, is consistent with the tumor's relationship to the spectrum of benign CD34-positive spindle cell neoplasms, which includes spindle cell and pleomorphic lipomas.

This case highlights a rare variant of pleomorphic fibroma, emphasizing that despite alarming cellular atypia, the lack of mitoses is a key feature favoring a benign diagnosis. Awareness of this entity's expanding morphologic spectrum is crucial for pathologists to distinguish it from its malignant mimics, thereby averting unnecessary aggressive therapy.