Pathology of Pleomorphic Fibroma

Dr Sampurna Roy MD                        2022

Pleomorphic Fibroma of the skin is a rare cutaneous fibrous tumor first described by Kamino et al in 1989.

Clinically presents as a slow-growing polypoid skin tag-like or dome shaped lesion in middle aged and elderly patients.

Site: On the trunk or extremities and rarely in head, neck, and subungual locations.

Microscopic features:

Well-circumscribed tumour composed of pleomorphic mononucleated and multinucleated cells with atypical nuclei with rare mitotic figures.

The cytologic pleomorphism is considered as a degenerative process as seen in a number of other mesenchymal tumours.

Immunohistochemistry:  CD34  positive. 

Desmin, Ki-M1p antibodies (pan-monocytic/macrophage marker) or S100 protein-Negative.

Staining for factor XIIIa has been patchy.

Differential diagnosis:

Benign tumours:  Dermatofibroma with atypical cells ; Giant cell fibroblastoma, pleomorphic lipoma ; sclerotic fibroma.

Malignant tumours: Undifferentiated pleomorphic sarcoma ; Atypical fibroxanthoma;

Limited local recurrence may occur but there have been no reports of regional extension or metastatic spread.