Characterization of Leiomyomatoid Angiomatous Neuroendocrine Tumour (LANT)-like Tumour in the Myometrium with Histopathological Examination.

Leiomyomatoid angiomatous neuroendocrine tumour (LANT) is possibly a new disease entity that was reported as a dimorphic neurosecretory tumour with a leiomyomatous vascular component; it was found in the pituitary. We describe uterine LANT-like malignant tumour in a 45-year-old woman with uterine mesenchymal tumour, diagnosed clinically as uterine leiomyoma. She underwent laparoscopic myomectomy. The tumour consisted of hyalinized vasculature, containing factor VIII-positive endothelium and α-smooth muscle actin-positive vascular smooth muscle cells, and stromal cells, expressing neuroadhesion molecules. Both vascular and stromal components diffusely expressed chromogranin A. Histopathological examinations of uterine LANT-like malignant tumour revealed the common characteristic abnormalities of malignant uterine mesenchymal tumours, i.e. leiomyosarcomas. From our research, defective expression of calponin H1 and proteasome β9 (PSMB9)/β1i is observed in uterine LANT-like malignant tumour similarly to immunopathological findings of uterine leiomyosarcoma. These findings meet the definition of uterine LANT-like malignant tumour, and the research findings of our clinical case suggest that LANT is a special type of neuroendocrine neoplasm and is not organ specific. Copyright