[Clinicopathological features of lymphoepithelioma-like carcinoma with abnormal expression of follicular dendritic cell markers: report of four cases].

<b>Objective:</b> To explore the clinical features, histopathological morphology, and differential diagnosis of lymphoepithelioma-like carcinoma with abnormal expression of follicular dendritic cell markers. <b>Methods:</b> From 2020 to 2021, 4 cases of lymphoepithelioma-like carcinoma with abnormal expression of follicular dendritic cell markers diagnosed in Fujian Cancer Hospital (2 cases) and the Second Affiliated Hospital of Fujian Medical University (2 cases) were collected. Different ancillary procedures such as HE, special stains, immunohistochemistry, and in situ hybridization techniques were used to assess the histopathological features and immunophenotypes. The clinical data were collected and literature was reviewed. <b>Results:</b> All 4 cases of lymphoepithelioma-like carcinoma with abnormal expression of follicular dendritic cell markers were male. They were 32, 45, 67 and 39 years old, respectively. The main clinical manifestations were bloody phlegm, abdominal pain, fatigue and anorexia. The clinical stages at diagnosis were stage Ⅳ (3 cases) and stage Ⅱ (1 case). Cases 2 and 3 had two pathological examinations at different sites, with a total of six pathological examinations. The histomorphology showed singly scattered or nests of tumor cells in a background of abundant small lymphocytes. The tumor cells were enlarged and pleomorphic, some appeared polygonal with inconspicuous cell borders, and they were arranged in a syncytial pattern. There were megakaryocytes, multinucleated tumor cells, and a few spindle-shaped cells seen. Atypical mitosis was commonly noted. By immunohistochemistry, the tumor cells were positive for CKpan(5/6), CK8/18(4/4), CAM5.2(2/5), CK-H(0/4), CK-L(3/4), EMA(4/5), CK5/6(3/6), p63(1/6), p40(1/6), E-cadherin (4/6), SSTR2(6/6), PD-L1(5/5), LCA(0/6), vimentin(5/6), CD2 (6/6), CD23(6/6), CD35(5/6), CXCL-13(4/5) and D2-40(1/5). The Ki-67 proliferative index was 60%-95%. In situ hybridization for EBER were all positive (6/6). Special stain for reticulin showed positive staining surrounding nests of tumor cells. <b>Conclusions:</b> The expression of follicular dendritic cell markers in lymphoepithelioma-like carcinoma is very rare, which may be related to EBV infection. Occasionally, it can overlap with follicular dendritic cell sarcoma by morphology and immunophenotype, which can lead to misdiagnosis. Only by combining clinical information, morphological characteristics and immunophenotype can an appropriate diagnosis be made.