A Rare Benign Mimicker of Malignancy: Cellular Spindled Histiocytic Pseudotumor of the Breast.

Cellular spindled histiocytic pseudotumor is a rare benign lesion composed of spindle-shaped histiocytes that may mimic malignant tumors, especially in extranodal sites such as the breast. We report a 56-year-old female patient presenting with a painful, palpable mass in the left breast accompanied by nipple discharge and skin changes. The patient had a history of previous benign excisional biopsies in the same region. Histopathological evaluation of a core needle biopsy revealed spindle-shaped histiocytic cells with mild nuclear atypia, and associated fat necrosis. Immunohistochemical analysis confirmed histiocytic differentiation (CD163, CD68, CD31 positive) and excluded epithelial, melanocytic, and stromal malignancies. These findings supported a diagnosis of cellular spindled histiocytic pseudotumor. Cellular spindled histiocytic pseudotumor of the breast is a rare and potentially misleading lesion that may clinically and radiologically mimic malignancy. Awareness of its histologic and immunophenotypic features is critical to avoid misdiagnosis and overtreatment. Accurate recognition may prevent unnecessary radical surgical or oncologic interventions.