Clinicopathological Challenge: Erythematous‐Yellowish Leg Plaques in a Young Woman: An Uncommon and Slowly Progressive Condition

A 24-year-old woman presented with a 4-month history of multiple firm erythematous-yellowish plaques on the posterior left leg; new similar lesions appeared over time. Skin biopsy showed a multinodular dermal and subcutaneous spindle and epithelioid cell neoplasm with focal hemorrhage, rhabdomyoblast-like features, and a mixed inflammatory infiltrate including neutrophils. Immunohistochemistry showed retained INI1 expression, diffuse nuclear FOSB expression, strong ERG positivity, diffuse cytokeratin AE1/AE3 positivity, negative CD34, and negative CAMTA1. Wide local excision with negative margins was performed, and no recurrence has been observed. This case underscores the diagnostic value of immunohistochemistry for distinguishing this condition from other tumors.