Lymphoepithelioma-like carcinoma of the endometrium: immunophenotypic characterization of a rare tumor with...

This report describes the clinicopathologic features of a primary lymphoepithelioma-like carcinoma of the endometrium, representing only the fourth reported case of this tumor at this location. In addition to its classic morphologic features, focal clear cells were also identified within the tumor, thereby expanding the morphologic spectrum of the neoplasm at this location. A comprehensive immunohistochemical characterization of the tumor was performed, as was microsatellite instability testing. The tumor was diagnosed in a 79-year-old woman and was surgically/pathologically staged as IB by the International Federation of Gynecology and Obstetrics (FIGO) criteria. The tumor displayed typical morphologic features (tumor cells with a syncytial appearance in an inflammatory background) with the exception of the aforementioned polygonal cells with well-defined cell membranes and cytoplasmic clarity in <1% of the tumor. The epithelial component showed strong and diffuse immunoreactivity for CAM 5.2, p53, p16, E-cadherin, cytokeratin (CK) 7, vimentin, CKAE1/3, and epithelial membrane antigen. The MIB-1 proliferative index in these regions was about 70%. Approximately 10% to 30% of lesional cells showed strong immunoreactivity for CK903, S100, MOC31, CD138, but the pattern of positivity was patchy and discontinuous. The epithelial cells were entirely negative for CK5/6, smooth muscle actin, p504S, CK20, synaptophysin, chromogranin, CD56, CD99, WT-1, thyroid transcription factor-1, p63, CD117 (c-kit), CD34, calretinin, desmin, estrogen receptor, progesterone receptor, FLI-1, ALK-1, D2-40, cytomegalovirus antigen, Epstein-Barr virus-encoded RNA-1, Epstein-Barr virus, monoclonal carcinoembryonic antigen, and HER2/neu. The foci with clear cells were not immunophenotypically distinct from the non-clear cell areas and had an approximately similar proliferative index. The inflammatory component was mixed (lymphocytes, histiocytes, plasma cells, neutrophils) but was composed predominantly of CD45/CD3/CD8 T lymphocytes, with a CD3 to CD20 ratio of approximately 10:1 and CD8 to CD4 T-cell ratio of approximately 3:1. Numerous (>100 positive cells per 10 high-power fields) S100-positive tumor-infiltrating Langerhans cells were present. The tumor DNA did not exhibit microsatellite instability at any of the loci analyzed. In summary, the limited data available suggest that lymphoepithelioma-like carcinoma is a distinct histotype of endometrial carcinoma that is typically seen in postmenopausal women, seems to be unrelated to the Epstein-Barr virus, and has an uncertain prognosis. Differential diagnostic and pathogenetic considerations are discussed within the context of the lesional morphologic and immunophenotypic profile as described herein and in previously reported cases.