RESUMEN
Undifferentiated nonkeratinizing carcinoma (UNC) is a poorly differentiated squamous cell carcinoma accompanied by a prominent reactive lymphoplasmacytic infiltrate that can occur in many anatomic sites. It shares morphologic features with undifferentiated nonkeratinizing nasopharyngeal carcinoma, in which a strong association with Epstein-Barr virus (EBV) has been noted. Among UNCs arising outside the nasopharynx, the linkage with EBV is variable; in particular, the few cases of UNC of the lip described thus far have been negative for EBV. This report describes a rare case of primary UNC of the lower lip mucosa in a 73-year-old man in whom molecular analysis for EBV showed some amount of viral DNA within the tumor. Surgical excision without adjuvant treatment was performed and the patient was alive without recurrence after 42 months of follow-up. This report presents a rare localization of UNC possibly related to EBV infection and with a good clinical outcome.