Retiform hemangioendothelioma. A distinctive form of low-grade angiosarcoma delineated in a series of 15 cases.

Fifteen cases of a distinctive type of low-grade angiosarcoma of the skin are described. Most tumors presented in the second to fourth decades of life, the youngest patient being 9 years old and the oldest 78 (mean age, 36 years). There was no sex predilection. Six tumors arose on the lower limb, four on the upper limb, three on the trunk, and one each on the penis and the scalp. One case arose in the setting of chronic lymphedema and another following radiotherapy for carcinoma of the uterine cervix. Distinctive morphologic features were the presence of long arborizing blood vessels arranged in a retiform pattern (reminiscent of normal rete testis) lined by monomorphic hobnail endothelial cells, a very prominent lymphocytic infiltrate in most cases, and the focal presence of papillae with hyaline collagenous cores, similar to those seen in malignant endovascular papillary angioendothelioma (Dabska's tumor). With a median follow-up of 7.25 years in 14 cases, retiform hemangioendothelioma has proved to be a low-grade neoplasm that recurs frequently but has a very low metastatic rate. The single regional lymph node metastasis in this series was from a case with a biphasic pattern in which only the spindle cell component was represented in the metastasis. There have been no tumor-related deaths, underlining the importance of accurate distinction from conventional angiosarcoma. This distinction is facilitated principally by the absence of dissection between individual collagen bundles and the absence of endothelial atypia or mitotic activity. The precise relationship between retiform hemangioendothelioma and Dabska's tumor is uncertain, possibly because cases of the latter may not be homogeneous.