Abstract
Atypical fibroxanthoma (AFX) is a cutaneous sarcoma with an assumed fibrohistiocytic differentiation. The tumor typically occurs on severely sun-damaged skin in the elderly. The tumors present as rapidly growing solitary papules or nodules. When a large AFX extends into the subcutaneous tissue, it raises a differential diagnosis of pleomorphic dermal sarcoma (PDS). Despite sharing histological similarities, AFX and PDS differ significantly in prognosis. AFX generally follows a benign course, whereas PDS is aggressive with higher recurrence and metastasis rates. The undifferentiated nature of AFX makes diagnosis challenging, as it requires an exclusion of other malignancies such as spindle cell melanomas and spindle squamous cell carcinomas. In this context, we present a case of AFX featuring a distinct variant characterized by a prominent myxoid stroma. A 63-year-old male presented with a pigmented 2.7 x 1.9 cm polypoid nodule on his left hand, showcasing asymmetry, irregular borders, and variegated coloration. A shave biopsy revealed a tumor composed of spindle, oval, and epithelioid cells, with atypical nuclei, multinucleation, foamy cytoplasm, and atypical mitotic figures. Solar elastosis was evident, with increased vascularity. The tumor was confined to the dermis without lymphovascular invasion. The tumor cells exhibited CD68 and CD10 positivity, with rare cells displaying CD31, SOX10, and AE1/AE3 positivity, while testing negative for CD34, Desmin, SMA, HHV8, S100, and Melan-A stains. Prominent myxoid stroma is present in the tumor, highlighted on alcian-blue staining. Notably, this myxoid variant is rare, with only sparse instances documented in literature.