"Benign" Metastasizing Fibrous Histiocytoma Harboring PRKCD Gene Fusions With Malignant Clinical Course

Area of Science:

• Dermatopathology
• Oncology
• Genetics

Background:

• Dermatofibroma/fibrous histiocytoma is a common dermal tumor.
• Subtypes like cellular and aneurysmal dermatofibroma have increased recurrence risk.
• Rarely, fibrous histiocytoma exhibits aggressive behavior with recurrence and metastasis.

Purpose of the Study:

• To describe two cases of benign fibrous histiocytoma with recurrence and metastasis.
• To highlight the importance of recognizing aggressive fibrous histiocytoma.
• To correlate complex chromosomal abnormalities with aggressive clinical behavior.

Main Methods:

• Case report of two patients with recurrent and metastatic fibrous histiocytoma.
• Identification of KIRREL1::PRKCD and LAMTOR1::PRKCD fusions in the respective cases.
• Review of clinical, pathological, and radiological findings.

Main Results:

• Patient 1: Cellular fibrous histiocytoma with KIRREL1::PRKCD fusion, recurrence, and metastasis to chest wall and thigh.
• Patient 2: Aneurysmal fibrous histiocytoma with LAMTOR1::PRKCD fusion, local recurrence, lymph node, and pulmonary metastasis.
• Both cases demonstrated clinically aggressive behavior despite typical benign morphology.

Conclusions:

• Fibrous histiocytoma rarely presents with aggressive behavior, recurrence, and metastasis.
• Accurate diagnosis, multidisciplinary management, and surveillance are essential for these rare cases.
• Complex chromosomal abnormalities may indicate an increased risk of aggressive clinical behavior in fibrous histiocytoma.