[Late-onset Epstein-Barr virus-positive diffuse large B-cell lymphoma at the same site after treatment of extranodal NK/T-cell lymphoma].

A 71-year-old man was diagnosed with extranodal NK/T-cell lymphoma (ENKTL) in 2008. He underwent chemoradiotherapy and achieved complete remission, with no relapse during follow-up (discontinued in 2013). In 2022, he presented with nasal obstruction and epistaxis, and ENKTL relapse was suspected because the lesion was localized to the original nasal site. However, histopathological examination of a biopsy specimen confirmed a diagnosis of Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma. Although both diseases are EBV-associated neoplasms, they derive from different lymphoid lineages and may arise metachronously at the same site. Careful differential diagnosis is essential because treatment strategies differ.