淋巴结树突状细胞肿瘤并非一定CK或者EMA阴性，老年人颈部淋巴结肿大当然首先除外转移癌，但FDC, IDC，CIRC也可以表达CK或者EMA，此例但从形态上看不除外这些肿瘤，前提是进一步检查鼻咽部，重新做CD21和CD35等。以下是几篇参考文献摘要：

AIMS: Tumours of dendritic/accessory cell origin are rare neoplasms arising in lymph nodes. Among these, tumours derived from cytokeratin-positive interstitial reticulum cells (CIRCs), a subset of fibroblastic reticulum cells, are reported even less frequently. The International Lymphoma Study Group (ILSG) has recently proposed a classification for tumours of histiocytes and accessory dendritic cells in which CIRC tumours are not included. We report a case of a CIRC tumour arising in a submandibular lymph node of a 66-year-old male. METHODS AND RESULTS: The neoplasm was composed of spindle cells with elongated or round nuclei, prominent nucleoli and abundant cytoplasm. These cells were arranged in a diffuse fascicular and vaguely whorled pattern. The tumour cells stained diffusely for S100, vimentin, desmin, lysozyme, and focally for CD68 and cytokeratins 7, 8, 18, CK-AE1 and CK-pool. Electron microscopy was performed for further evaluation on samples taken from the paraffin block; this revealed cytoplasmic projections and rudimentary cell junctions. CONCLUSIONS: Histopathologist should be aware of the existence of tumours deriving from CIRCs, as these cases may be misdiagnosed as metastatic carcinoma. Careful clinical and pathological evaluation is necessary to exclude this possibility.

BACKGROUND: Follicular dendritic cell (FDC) tumors are rare. A majority of the reported cases were confined to the lymph nodes. We report a case of FDC tumor occurring in the parapharyngeal region in a 45-year-old woman. METHODS: Characteristic histopathologic features of the excised primary and recurrent parapharyngeal tumors in conjunction with immunohistochemistry and electron microscopy helped us to arrive at a diagnosis of FDC tumor. RESULTS: Histopathology of primary excision revealed a lobulated tumor with a suggestion of ill-defined whorls. The most striking feature was regular occurrence of aggregates of lymphocytes within the tumor, especially around the blood vessels. The anatomic location together with the histology indicated the possibilities of either a meningioma, a salivary gland tumor, or a nerve sheath tumor. Immunostains for cytokeratin (CK), S-100 protein, and smooth muscle actin (SMA) were negative. However, the tumor cells showed strong immunoreactivity for epithelial membrane antigen (EMA) and vimentin. A diagnosis of parapharyngeal meningioma appeared to be the closest possibility. One year later, the patient developed a recurrence at the same site. A reexcision showed an identical tumor with an additional feature of lymphatic embolization and angioinvasion. A review of the entire case with further immunoreactivity for CD21 and CD35 confirmed the diagnosis of FDC. CONCLUSIONS: Follicular dendritic cell tumor has distinctive morphologic features and immunohistochemical profile. It is also characterized by considerable potential for recurrences.

 学习！谈谈自己的思路。

老人，可疑淋巴结内的双相性肿瘤。依次鉴别：

转移（癌，恶黑）

软组织肉瘤（滑膜肉瘤）

淋巴瘤（FDC/IDC，NHL）

免疫组化支持癌。但不知道CD68和S-100哪些细胞阳性。