Radiation-Induced Angiosarcoma of the Breast With Diffuse GATA-3 Positivity: A Possible Diagnostic Pitfall

Radiation-induced angiosarcomas of the breast are rare malignancies that carry a poor prognosis. Expected immunohistochemical profiles reflect vascular differentiation: CD31 and ERG positivity, with variable CD34 positivity. GATA-3 is a transcription factor important for mammary gland development, playing a role in ductal epithelial cell differentiation. It serves as an important immunohistochemical marker of breast-origin carcinomas and is not associated with angiosarcomas. We report a case of an 83-year-old woman with breast radiation-induced angiosarcoma, which displayed diffuse GATA-3 positivity, which has not been previously reported in the literature. The patient had a history of inflammatory carcinoma of the left breast (histologically a high-grade invasive ductal carcinoma of no special type) treated with lumpectomy and radiation therapy. Ten years later, she presented with skin thickening and 3 tender nodules (ranging from 0.6 to 2 cm) confined to the left breast skin. Biopsy showed a high-grade, epithelioid dermal neoplasm with abundant hemorrhage. The tumor was diffusely positive for GATA-3, CD31, and ERG, with focal CD34 positivity. Strong and diffuse MYC positivity with an increased Ki-67 proliferative index was also demonstrated. CK5/6, AE1/AE3, MOC-31, CK5/6, CK7, ER, PR, S100, Melan A, and synaptophysin were all negative. The histopathologic features and immunohistochemical profile were consistent with radiation-induced angiosarcoma. With this case, we highlight a diffusely positive GATA-3 staining pattern in radiation-induced angiosarcoma of the breast, which has not been previously documented. Awareness of this potential staining pitfall is essential for arriving at the correct diagnosis particularly when recurrent or metastatic high-grade carcinoma is a diagnostic consideration.