ABSTRACT
Plexiform fibrohistiocytic tumor (PFHT) is a rare mesenchymal neoplasm of intermediate malignancy and possibly of myofibroblast origin. It is morphologically divided into 3 groups: cellular, fibrous, and mixed. A 4-year-old girl presented with an irregular shaped subcutaneous mass on her left popliteal fossa for 6 months. The biopsy specimen showed multinodular tumor islands extending from dermis to subcutaneous layer, composed of histiocytes and osteoclast-like multinucleated giant cells, and circumscribed by fibrous tissue. Immunohistochemical staining was positive for CD68 in giant cells and histiocyte-like cells within tumor islands and faintly positive for smooth muscle actin around nodules. A cellular variant of PFHT was eventually diagnosed. Although PFHT comprises morphologically normal cells, it has the biological potential for malignant change and distal metastasis. Therefore, PFHT is categorized as a neoplasm of intermediate malignancy, and wide total excision with close follow-up is crucial.