Stewart–Treves syndrome arising in chronic postmastectomy lymphedema: A clinicopathologic case report

Stewart–Treves syndrome (STS) is a rare and highly aggressive secondary cutaneous angiosarcoma that develops in the setting of chronic lymphedema, most commonly following mastectomy and axillary lymph node dissection for breast cancer. Because its early clinical manifestations frequently mimic benign conditions such as hematoma, cellulitis, or vascular proliferations, diagnosis may be delayed, adversely affecting patient outcomes. We report the clinicopathologic features of an 81-year-old woman who developed multifocal hemorrhagic papules and nodules on a chronically lymphedematous upper extremity eight years after mastectomy and axillary lymph node dissection for invasive ductal carcinoma of the breast. Histopathologic examination demonstrated an infiltrative malignant vascular neoplasm composed predominantly of atypical spindle cells with irregular anastomosing vascular channels and focal vasoformative areas extending from the dermis into the subcutaneous tissue. Immunohistochemical analysis showed diffuse strong CD31 and CD34 expression, confirming endothelial differentiation. The combination of the characteristic clinical presentation, longstanding postmastectomy lymphedema, and histopathologic findings established the diagnosis of Stewart–Treves syndrome. This case highlights the importance of maintaining a high index of suspicion for newly developed hemorrhagic or violaceous cutaneous lesions arising within chronically lymphedematous tissue. Prompt biopsy, careful clinicopathologic correlation, and immunohistochemistry for endothelial markers are essential for establishing an early diagnosis and facilitating timely multidisciplinary management of this highly aggressive malignancy.