━━ Background. Lymphoepithelioma-like carcinoma (LELC) is a rare tumor that has features that are similar to lymphoepithelioma of undifferentiated nasopharyngeal carcinoma. Case. A 65-year-old man had undergone radiotherapy for prostate cancer five years previously. The patient was referred to our institution after the detection of a nodule in the left lower lobe of the lung by follow-up computed tomography (CT). Since the tumor had increased in size, we performed thoracotomy and open biopsy. A

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... frozen-section examination revealed undifferentiated carcinoma, and left lower lobectomy was performed. A histological examination revealed irregular nests of atypical cells with large nuclei, and significant lymphocytic infiltration in the stroma of the tumor. A histological examination with hematoxylin-eosin staining revealed features similar to LELC of the lung. According to the World Health Organization classification (4th edition), a diagnosis of LELC requires infection by Epstein-Barr virus (EBV). However Epstein-Barr virus-encoded RNA in situ hybridization (EBER-ISH) and immunohistochemical staining for latent membrane protein 1 (LMP1) were negative in this case. Thus, due to the lack of EBV infection, the pathological diagnosis was non-keratinizing squamous cell carcinoma with marked inflammatory cell infiltration. At the time of writing, the patient has been recurrence-free for fifteen months. Conclusion. We experienced a case of non-keratinizing squamous cell carcinoma that showed pathological features that were similar to pulmonary LELC. A careful diagnosis is required because LELC and undifferentiated carcinoma have significantly different prognoses. Further studies are warranted to determine how to diagnose and treat EBV-negative cases that show findings similar to LELC.