A Giant, Deep, Benign Fibrous Histiocytoma with a Palisading Pattern

Dear Editor: A 42-year-old male patient presented to our clinic with a skin-colored mass that had been present for 2 years; his medical and family histories were otherwise unremarkable. Physical examination revealed a soft, movable, skin-colored mass on his upper left back, with a brown, bean-sized pedunculated nodule on the overlying skin (Fig. 1A). Excisional biopsy was performed. The tumor, which was well demarcated and localized in the subcutaneous layer, measured 5.4×5.1×2.1 cm (Fig. 1B). The histopathological examination indicated that the lesion was an encapsulated mass, located in subcutaneous tissue with a central cavity. The tumor was well-circumscribed by a fibrous capsule, and no honeycomb pattern was observed in the marginal area. In the tumor periphery, large blood vessels with a dilated, branching appearance were observed (Fig. 2A). The tumor cells were arranged in a palisading and partially storiform pattern, with focal myxoid change (Fig. 2B). Under high magnification, the tumor cells were spindle shaped with elongated nuclei and an ill-defined cytoplasm; individual cells were infiltrating between collagen bundles and arranged in a palisading pattern, similar to Verocay bodies (Fig. 2C). Cellular atypia and mitotic bodies were not detected. Immunohistochemical analysis revealed that the cells were strongly positive for CD34 (Fig. 2D); focally positive for factor XIIIa; and negative for S-100 (Fig. 2E), desmin, actin, and CD68. A diagnosis of giant, deep, benign fibrous histiocytoma (BFH), with a palisading pattern, was rendered, with no evidence of recurrence at 15 months after excision. Fig. 1 (A) A skin-colored mass on the back (arrows) with a coincident overlying skin tag (inset: close-up view). (B) The excised 5×5×2 cm well-encapsulated erythematous oval mass. Fig. 2 (A) Scanning view of the histopathological examination of the lesion showing an encapsulated mass located from the lower dermis through the subcutaneous tissue with a central cavity. The tumor was well circumscribed by a fibrous capsule, and no honeycomb ... BFH, which is characterized by several histological subtypes, is among the most-common soft tissue skin tumors. Since Fletcher's1 description in 1990 of 21 cases of deep BFH (DBFH), several more cases have been reported1,2,3. DBFH, which accounts for <1%~2% of all BFH cases, is larger and arises lower in the subcutis1, and confers an increased risk of local recurrence and distant metastasis3. Similar to BFH, giant fibrous histiocytoma (>5 cm), which represents a rare variant of fibrous histiocytoma, is benign, and no local recurrence after surgical excision has been reported to date4. Palisading BFH is a rare variant of BFH, first described by Schwob and Santa Cruz5 in 1986. On histopathological examination, palisading BFH resembles a schwannoma; the lack of neural cells and S-100 negativity could facilitate the differential diagnosis5. Although several cases of palisading BFH have been reported2,5, only one case of palisading DBFH has been documented2. In our patient, the tumor cells were strongly positive for CD34; therefore, it is difficult to exclude dermatofibrosarcoma protuberance. However, Gleason and Fletcher3 reported that 40% of DBFH cases are positive for CD34. The histopathological findings of a well-circumscribed capsule, low cell density, and a lack of atypical cells and mitotic bodies also suggest a benign nature; therefore, the final diagnosis was an uncommon case of giant DBFH.