[Angiomatosis of the breast: a clinicopathological analysis of six cases].

<b>Objective:</b> To investigate the clinicopathological features and differential diagnosis of breast angiomatosis. <b>Methods:</b> Six cases of breast angiomatosis diagnosed at the Department of Pathology, the Seventh Medical Center, People's Liberation Army General Hospital and the Department of Pathology, Dongzhimen Hospital, Beijing University of Chinese Medicine from January 2011 to December 2023 were evaluated and reviewed. <b>Results:</b> All patients were female with an average age of 46 years at presentation, ranging from 25 to 62 years. The most common clinical presentation was a palpable unilateral breast mass with diameter ranging from 7 to 14 cm, and the average size was 11 cm. Histologically, all cases were composed of variably-sized ectatic, thin-walled blood vessels with minimal to no apparent smooth muscle, lined by flat normochromic endothelium without atypia, and diffusely infiltrating the breast stroma. Where present, the lesional vessels infiltrated between and around terminal duct lobular units but not into individual intralobular stroma. Immunohistochemical staining for CD31, CD34, Factor Ⅷ, Fli-1 and D2-40 revealed positive expression in vascular and/or lymphatic endothelial cells. Additionally, the Ki-67 proliferation index was found to be less than 1%. <b>Conclusions:</b> Angiomatosis of the breast is a rare benign vascular lesion. Distinguishing it from low-grade angiosarcoma requires careful consideration of the growth pattern, atypical features, and Ki-67 proliferation index.