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Case Reports

Abstract

Acral fibrochondromyxoid tumor (AFCMT) represents a distinctive subset of acral soft tissue neoplasms, typically manifesting on the digits, characterized by a rich stroma displaying fibrous, chondroid, and myxoid elements. We report a case of a 77-year-old female presenting with an asymptomatic lesion on the left index finger, initially clinically suspected to be a digital mucous cyst. Histopathological examination revealed a well-circumscribed dermal neoplasm made of bland ovoid to round cells with nuclear grooves, reminiscent of chondrocytes, amidst abundant myxoid to chondromyxoid stroma with focal myxoid degeneration. No cytologic atypia, increased mitotic activity, or necrosis were identified. Immunohistochemical analysis demonstrated strong and diffuse CD34 and ERG staining, while S100, SMA, keratin, and desmin were negative. These morphological and immunophenotypical characteristics are consistent with acral fibromyxoid tumor. Clinically, AFCMTs typically present as small soft tissue masses near the phalanges of fingers and toes. Histologically, they exhibit a multinodular growth pattern, with cells displaying features reminiscent of chondrocyte differentiation. Despite their histological complexity, AFCMTs lack aggressive morphological or clinical features, supporting their benign nature. Molecularly, AFCMTs commonly harbor THBS1::ADGRF5fusions, with THBS1 encoding a member of the extracellular matrix glycoproteins. We aim to raise awareness among dermatopathologists regarding the existence of AFCMT and their potential encounter during sign-out. While AFCMTs may mimic other lesions, such as soft tissue chondromas or myoepithelial neoplasms, their distinct histological and immunohistochemical features aid in accurate diagnosis and management. Recognizing AFCMT's distinct characteristics is essential to prevent misdiagnosis and avoid overtreatment, underscoring the need for further awareness.