Primary mesenteric malignant mixed mesodermal (müllerian) tumor with neuroendocrine differentiation.

Extragenital malignant mixed mesodermal (müllerian) tumors (MMMT) are rare neoplasms, with but 24 well documented cases in the literature. Neuroendocrine differentiation in mixed müllerian neoplasms has been mentioned only anecdotally. We report on the clinical, pathological, and immunohistochemical features of a hitherto-undescribed extragenital MMMT with prominent neuroendocrine differentiation arising from the jejunal mesentery. This lesion was composed of a poorly differentiated epithelial component and a spindle cell component with heterologous (rhabdomyoblastic) differentiation. The bulk of the tumor consisted of small cell neuroendocrine carcinoma, which exhibited strong immunoreactivity for NSE, LEU-7, chromogranin A and synaptophysin. Electronmicroscopy confirmed the presence of neurosecretory dense-core granules. The primary mesenteric origin of the tumor was established at autopsy. Along with a brief review of previously reported extragenital MMMT some histogenetic concepts relevant to this case are discussed.