Papillary endothelial hyperplasia arising in the irradiated breast: A diagnostic dilemma.

Papillary endothelial hyperplasia (PEH) is a benign proliferative lesion that may occur in any site of the body, but most commonly affects the skin and subcutaneous tissues. In the breast, PEH has been documented but is rare. PEH is notorious for being misdiagnosed as angiosarcoma due to its complex growth pattern, papillary processes and interlacing vascular channels. The occurrence of PEH years after breast irradiation constitutes a pathological and clinical diagnostic challenge because angiosarcoma is far more common in this setting. The most important features that differentiate papillary endothelial hyperplasia from angiosarcoma are its presentation as a round nodule without infiltrative borders, its localization inside a vessel or in association with thrombus, and the lack of significant cytologic atypia or areas of solid growth, even in the presence of a complex architecture. Clinical history and site of involvement (cutaneous versus parenchymal) are usually of help to establish a correct diagnosis. Herein, we describe two cases of PEH presenting in patients with history of breast carcinoma and breast radiation therapy. The clinical and morphological features as well as the differential diagnoses are discussed. To our knowledge, no other cases of PEH of the breast occurring in the post-radiation setting have been described in the literature.