Clinicopathologic and immunohistochemical study of breast angiosarcoma

Breast angiosarcoma (AS) is a rare malignancy which can be classified into primary or secondary as a result of breast cancer therapy. On histology, breast AS has a wide spectrum of morphologic presentations, and its diagnosis can be challenging based on morphologic evaluation alone. Here, we studied 10 cases of breast AS diagnosed at our institution during a 20-year period, in which 7 cases were radiation-associated AS (RA-AS) and 3 cases were primary AS (P-AS). The average latency between radiotherapy and RA-AS was 8.1 years. RA-AS mostly occurred in breast skin, while all P-AS involved breast parenchyma. All 10 AS cases were high grade, including 4 RA-AS cases demonstrating epithelioid morphology. Histologic morphologies of AS varied from confluent growth of atypical spindle or epithelioid cells to scattered marked pleomorphic cells. Some cases appeared deceptively bland or low grade, but the presence of areas of haemorrhage ('blood lake') or necrosis upgraded them to high grade lesions. Additionally, some epithelioid RA-AS cases with lymphatic differentiation (D2-40 positive) showed pseudopapillary morphology characterized by discohesive cells sloughing off at periphery of vascular cores, resembling papillary breast carcinoma. P-AS did not show prominent vesicular nuclei and/or conspicuous nucleoli, which were features observed in RA-AS. C-MYC immunostain results showed P-AS was completely negative or focal weakly positive in hypercellular areas. In comparison, RA-AS were consistently positive for c-MYC. Epithelioid RA-AS with lymphatic differentiation tended to show stronger and/or more diffuse c-MYC positivity than other AS cases. CD31 and ERG immunostains showed positivity in all cases, while CD34 were negative in some cases with lymphatic differentiation. This study offers a detailed morphologic and immunohistochemical assessment of a rare tumor of the breast that is important to recognize. Common differential diagnosis for breast AS, including post-radiation atypical vascular proliferation (AVP), are also reviewed and discussed.