Papillary Endothelial Hyperplasia in Late Post-Radiation or Late Post-Operative Breast Hematomas Mimicking Angiosarcoma.

Women treated for breast cancer with lumpectomy and radiation therapy are at risk for disease recurrence, as well as radiation-associated (secondary) angiosarcoma. Hematomas are rarely responsible for new masses in this setting. We examined a series of breast hematomas with papillary endothelial hyperplasia (PEH), some of which raised concern for angiosarcoma, to identify features that aid in distinguishing these benign lesions from angiosarcoma in diagnostically challenging cases. Hematomas diagnosed in twenty-eight breast biopsy and/or resection specimens from nineteen women within our institutional archive were studied (2013-2026). Clinical, imaging, and pathology data were correlated. Immunohistochemical evaluation included PRAME, MYC, p53 and ERG IHC, along with Martius-Scarlet-Blue (MSB) histochemical staining. The mean age at hematoma presentation was 72.4 years, with patients presenting long after surgery (mean: 18 years) and radiotherapy (mean: 13.2 years). Several patients were on medications interfering with coagulation (13). Most masses were categorized as BI-RADS 4 and underwent multiple diagnostic procedures. In hematomas, reactive endothelium dissected organizing fibrin rather than collagen, highlighted by MSB or trichrome stains. PRAME was negative while MYC and p53 demonstrated wild type expression in all tested lesions. With the breast cancer survivor population increasing in number, age, and use of anti-coagulation, late breast hematomas are increasingly encountered by breast pathologists and radiologists. Careful evaluation to distinguish organizing hematoma with PEH from angiosarcoma is necessary.