Hemosiderotic Fibrolipomatous Tumor

To the Editor:

Hemosiderotic fibrolipomatous tumor (HFLT) formerly known as hemosiderotic fibrohistiocytic lipomatous tumor is a more recently described locally aggressive entity within the spectrum of fibrous lesions involving the subcutaneous tissue.^1–3 As its name implies, it is characterized by a proliferation of fibroblast-like spindle cells and adipocytes accompanied by hemosiderin deposition. It most commonly occurs as a slowly growing, bluish atrophic plaque at the dorsal aspect of the foot or ankle in middle-aged adults of either sex, women being slightly more involved than men. Previous local trauma may play a role in the etiology but has not been proven. Rather, the lesion is now considered to be neoplastic in nature with a typical chromosomal translocation t(1;10)(p22;q24).^4,5 Since the original description in 2000,¹ a total of around 40 cases have emerged in the literature, mostly pathology journals. The entity is extraordinary rare, and the dermatologist/dermatopathologist may be the initial physician to be consulted with this soft-tissue tumor and should therefore be aware of it.

In the following, we report on a 45-year-old woman with a 4-year history of a gradually growing, slightly atrophic bluish-green plaque with moderate telangiectasia measuring 14 × 6 cm at the dorsum of the left foot extending to the ankle (Fig. 1). There is no definite evidence for a previous trauma. The patient is otherwise in good health, and routine investigation, including chest x-ray, abdominal ultrasound, and blood count, did not reveal any abnormalities. Histopathologically, there is an ill-defined proliferation of bland spindle cells with vesicular nuclei and indistinct nucleoli and well-differentiated adipocytes in the subcutaneous tissue. The spindle cells grow in whorls and fascicles intersecting the adipocytic component accompanied by prominent hemosiderin deposition both within the fibroblast-like cells and macrophages as well as extracellularly. Immunohistology reveals the spindle cell component to be positive for CD34 and negative for S-100 protein, smooth muscle actin, desmin, and CD68 (Fig. 2). After intensive information and discussion with the patient, she decided not to undergo any surgery at present but instead follow a wait and see regimen with quarterly controls including local computed tomography and magnetic resonance imaging. Clinical follow-up of 1.5 years did not show significant growth or evidence for metastatic spread.

FIGURE 1.: Slightly atrophic bluish-green plaque (14 × 6 cm) at the dorsum of the left foot and above the ventral ankle region. Note the hematoma-like character and prominent telangiectasia. Centrally, there is a small scar after biopsy.

FIGURE 2.: Histopathologically, there is an ill-defined proliferation of bland spindle cells that grow in fascicles and whorls dissecting the adipocytic component. The latter represent mature adipocytes devoid of atypia (A, B). There is prominent hemosiderin deposition (Prussian blue stain, C). Fibroblast-like cells are negative for S-100 protein while adipocytes are positive. Prominent brown hemosiderin is evident as well (D).

The so-called “fibrohistiocytic” lesions may be purely dermal, dermal/subcutaneous, or solely subcutaneous in location. In addition, the fibroblastic component may be reactive as in most dermatofibromas or neoplastic in nature. Depending on the location of the reactive or neoplastic process with the presence of varying anatomical structures with spindle cell morphology, diverse lesions enter the differential diagnosis.

With respect to the subcutaneous location of HFLT, it may be challenging to rule out especially dermatofibrosarcoma protuberans, plexiform fibrohistiocytic tumor, spindle cell lipoma, or well-differentiated liposarcoma in a small biopsy. Apart from the clinical information, immunohistology may be helpful to come to a definite diagnosis. However, it is in general mandatory to evaluate the architectural growth pattern in a large representative biopsy. The histopathological features are then distinctive with an ill-defined proliferation of monomorphous fibroblast-like cells and adipocytes accompanied by hemosiderin, which have led to the initial description of HFLT in a series of 10 cases.¹

Clinically, the tumor may imitate a long-standing hematoma or angiomatoid fibrous histiocytoma.⁶ The clinical course is benign but may be locally aggressive. In those cases, as in our, where complete excision is impossible, clinical follow-up is advisable because the spindle cell component—but interestingly not the adipocytic one—has been reported to have the capacity of malignant transformation into more aggressive sarcoma in general or myxoinflammatory fibroblastic sarcoma in particular.^3,5,7,8 The adipocytic component that is a prominent part of HFLT may therefore only be an innocent bystander. This assumption is supported by the well-differentiated morphology of the adipocytes in HFLT also confirmed in previous studies.^1,2

From a molecular genetic point of view, HFLT and myxoinflammatory fibroblastic sarcoma share the identical chromosomal translocation t(1;10)(p22;q24) with the fusion gene TGFBR3-MGEA5.^4,5,7 Recently, rearrangements of TGFBR3 and/or MGEA5 have also been identified in pleomorphic hyalinizing angiectatic tumors with histopathological features of HFLT suggesting a close relation between these 3 entities.⁸ Thus, molecular genetic investigation is an important adjunct method in small biopsies or difficult cases, although negative results may occur.

In conclusion, HFLT belongs to the expanding group of translocation-associated mesenchymal tumors with distinct histopathological features involving fibroblast-like cells and adipocytes. Despite advances in immunohistochemistry and molecular genetic investigations, the overall histopathological architectural growth pattern together with the clinical presentation is essential to come to a definite diagnosis.