Post-mastectomy benign lymphangioendothelioma of the skin following chronic lymphedema for breast carcinoma: a teaching case mimicking low-grade angiosarcoma and masquerading as Stewart-Treves syndrome

Benign lymphangioendothelioma (BL) represents a very rare lymphatic vascular proliferation. Our aim is to be aware that owing to its characteristic features, pathologists can easily misinterpret it as cutaneous low-grade angiosarcoma when examining only small specimens. In the present case, multiple small and yellowish to reddish soft nodules were noticed in the edematous left arm of a 54-year-old Japanese female 4 years after the radical mastectomy with axillary lymph nodes dissection and following radiotherapy to the chest for the left breast carcinoma. The biopsy specimen showed an ill-defined lesion composed of a proliferation of irregular and sometimes anastomosing vascular structures in the dermis, lined by endothelial cells having mildly hyperchromatic and pleomorphic nuclei, but no mitotic figures. As the lesion grew within deeper dermis, these proliferating vessels dissected dermal collagenous bands, occasionally arranged in low-papillary projections and/or characteristic hobnail cytomorphology. We first interpreted it as low-grade angiosarcoma following chronic lymphedema due to the operation, i.e., the so-called Stewart-Treves syndrome. Although additional treatments were performed for 7 years, she had neither local invasion nor metastases of these tumors, respectively, and was alive and well. Retrospective immunohistochemical findings demonstrated that these mildly atypical endothelial cells were strongly positive for lymphatic vessel endothelial hyaluronan receptor (LYVE)-1 as well, and MIB-1 labeling index was less than 1%. Therefore, we finally made a diagnosis of BL of the skin. MIB-1 labeling index might be useful and adjunctive aids for reaching the correct diagnosis of cutaneous BL, especially in case of small or inadequate specimens.