Abstract

We present a case of a 27-year-old gentleman with a gradually enlarging subcutaneous nodule on the lower medial leg. The nodule exhibited occasional erythema but was rarely painful. Excisional biopsy revealed a well-circumscribed neoplastic proliferation involving the deep dermis and subcutis. Histologically, the tumor exhibited myxoid and dense areas. The myxoid area showed fascicles of bland spindle cells with a myxoid background, while the dense showed an atypical spindle cell infiltrate with mild to moderate cytologic atypia. Immunostains revealed focal positivity for cytokeratin AE1/AE3, strong and diffuse CD34 expression, and focal SMA positivity. The tumor was negative for several markers, including SOX10, S100, Desmin, D2-40, CD10, ALK1, MUC4, and MDM2.     Based on the histopathologic findings and immunostains, the diagnosis of Superficial CD34-positive Fibroblastic Tumor (SCD34FT) was made. SCD34FT is a rare neoplasm primarily affecting the lower extremities, with a low-grade behavior and a tendency to involve the dermis and subcutis. The differential diagnosis includes other spindle cell entities based on site, morphology, and immunostains. While our case showed some atypical features, like myxoid areas, the immunophenotypic profile, including CD34 and keratin expression, supported the diagnosis. Additionally, WT1 expression further supported the diagnosis. SCD34FT is a recently recognized entity that expresses diffuse CD34, and it may show patchy expression of keratin and desmin. Positive expression of CADM3 and PRDM10 rearrangement further confirms the diagnosis. Despite pleomorphism and cytologic atypia, SCD34FT exhibits low mitosis and has a low-grade behavior. Our patient showed no recurrence after 1 year, supporting the indolent nature of this tumor. Awareness of this distinctive neoplasm and its characteristic features is essential for accurate diagnosis and appropriate management.