A leiomyomatoid angiomatous neuroendocrine tumor of the myometrium: case study with ultrastructural analysis.

Leiomyomatoid angiomatous neuroendocrine tumor (LANT) is a possible new disease entity that was described as a dimorphic neurosecretory tumor with a leiomyomatous vascular component; it was found in the pituitary. We describe here a second case of LANT in a 45-year-old woman with a myometrial tumor, diagnosed clinically as uterine leiomyoma. She underwent laparoscopic myomectomy. The tumor consisted of hyalinized vasculature, containing factor VIII-positive endothelium and smooth muscle actin-positive vascular smooth muscle cells, and stromal cells, expressing neuroadhesion molecules. Both vascular and stromal components diffusely expressed chromogranin A and, as evidenced by electron microscopy, possessed smooth muscle actin filaments and electron-dense neurosecretory granules, which contained the neurosecretory hormone somatostatin. Although no cytokeratin-positive cells were observed, some tumor cells had positive Grimelius staining for argyrophilic granules. These findings meet the definition of LANT, and the occurrence of our case suggests that LANT is a special type of neuroendocrine neoplasm and is not organ specific.