Primary Angiosarcoma of the Breast Diagnosed on Core Needle Biopsy: A Diagnostic Challenge

Primary angiosarcoma of the breast is very rare and difficult to pathologically diagnose especially on core needle biopsy. Only 11 cases of breast primary angiosarcoma diagnosed on core needle biopsy have been reported in English literature of last 5 years. We reported a case of primary angiosarcoma of the breast diagnosed on core needle biopsy and summarized the useful morphological clues in literature which prompted the diagnosis of angiosarcoma. A 50-year-old woman presented with a palpable mass in her left breast for a year. She never received breast surgery or radiotherapy before. Microscopically, the core needle biopsy specimen displayed interanastomosing vascular spaces that dissected through the mammary stroma and adipose tissue. The vascular channels were mostly lined by a single layer of endothelial cells with a mild degree of nuclear atypia, whereas focally, the endothelia were multilayered, with tufting and formation of glomerulus-like structures. CD31, CD34, and ERG immunochemical stain highlighted the endothelial cells lining on the vascular spaces. The Ki67 index was about 10%, and MYC was negative. Primary angiosarcomas have significant overlaps of morphological features with benign and borderline vascular lesions. Anastomosing vascular spaces, cytologic atypia, endothelial mitotic activity, infiltration of glandular parenchyma, elevated Ki-67, and high cellularity are all useful clues to diagnose angiosarcomas. Among them, anastomosing vascular spaces with infiltrated growth pattern especially invasion into the breast intralobular stroma and adipose tissue was the most common character of angiosarcomas which alert the possibility of malignancy in core needle biopsy. However, an accurate diagnosis demands integration of various histological clues and multidisciplinary discussion.