Superficial low-grade fibromyxoid sarcoma

Abstract

Background: Low-grade fibromyxoid sarcoma (LGFMS) typically involves deep soft tissue (beneath the fascia) of the proximal extremities and trunk. Long-term follow-up has shown a high rate of local recurrence, metastasis, and death. To the best of our knowledge, there is only one previous large series focusing on superficial LGFMS suggesting superficial tumors are disproportionately more common in children and may have a better prognosis. Our study's primary goals are to confirm these findings and increase general awareness that LGFMS may arise in superficial soft tissue.

Methods: We retrieved our cases of superficial LGFMS diagnosed between 2008 and 2020. Available slides were reviewed, and clinical data and follow-up information were obtained.

Results: The patients included nine males and 14 females with a median age of 29 years; eight (35%) were children (<18 years) and five (22%) were young adults (18-30 years). The majority involved the lower extremities (65%). The tumors were primarily centered in the subcutis (91%) and dermis (9%). Microscopically, they had typical features of LGFMS with alternating fibrous and myxoid zones composed of bland, slightly hyperchromatic spindled cells. All were positive for MUC4 by immunohistochemistry and/or FUS rearrangement by FISH. Follow-up on 14 cases ranged from 11 to 148 months (median 61 months) with no evidence of recurrences or distant metastases.

Conclusions: Compared to conventional deep-seated counterparts, superficial LGFMS is more likely to occur in the extremities of children and young adults and may have a better clinical outcome. Further studies with longer follow-up will likely help support these findings.

Keywords: Evans tumor; immunohistochemistry; low-grade fibromyxoid sarcoma; skin neoplasms; superficial.

FIGURE 1

Superficial low‐grade fibromyxid sarcoma. Superficial low‐grade fibromyxoid sarcoma is confined to the superficial soft tissue without fascial or skeletal muscle involvement—Case 4 (A). There are alternating fibrous and myxoid zones with abrupt transition with a swirling, whorled growth pattern—Case 15 (B). The tumor vasculature consists of small branching to curvilinear vessels—Case 1 (C). There were also arteriole‐sized vessels with perivascular sclerosis—Case 15 (D). The neoplastic cells are very bland with spindled morphology in fibromyxoid stroma—Case 2 (E). There were hypercellular areas with sheets of cells with moderate pleomorphism—Case 12 (F). (H&E; A, scanned image; B, ×25; C and D, ×100; E and F, ×200)

FIGURE 2

Unusual features of superficial low‐grade fibromyxoid sarcoma. Case 9 shows an increased number of mitotic figures and increased cellularity with mild pleomorphism and vaguely stroriform pattern (A). There is also an area of coagulative necrosis (B). Case 11 displays a prominent hyalinized sclerotic collagen matrix that is associated with bland cells in vague cords resembling sclerosing epithelioid fibrosarcoma (C). This case also exhibits multiple multinucleated giant cells (D) with osseous metaplasia (E). (H&E; A, ×200; B, ×100; C, ×200; D, ×100; E, ×80)

FIGURE 3

An immunohistochemical for MUC4 shows diffuse and strong positivity within the lesional cells (IHC; ×200).