Extranodal natural killer (NK)/T-cell lymphoma, nasal type (ENKTL) is an aggressive lymphoma usually of NK, or less commonly, T-cell origin. ENKTL most frequently affects the upper aerodigestive tract, followed by skin and gastrointestinal tract.1 ,2 It is characterised by vascular damage and destruction, prominent necrosis, cytotoxic immunophenotype and association with Epstein–Barr virus (EBV).1 ,2 The size of the neoplastic cells is variable, ranging from small/medium to large.1 ,2 Phenotypically, the neoplastic cells express cytoplasmic CD3, cytotoxic markers and frequently NK-cell marker CD56. The expression of CD20, a B-cell antigen, is exceptional in ENKTL. In this report, we present the case of a primary gastric ENKTL with a subcutaneous relapse and acquisition of CD20 expression, while the initial diagnostic gastric tumour was CD20 negative.

A 48-year-old Taiwanese man presented with abdominal discomfort, fever and tarry stool in a regional hospital in April 2014. Body weight loss of 8 kg in 3 months was also noted. Endoscopic examination revealed a huge ulcer over the greater curvature side of the gastric body and CT scans showed thickening of the gastric wall. Endoscopic biopsy showed an ulcerative tumour comprising small-sized to medium-sized atypical lymphocytes expressing CD3 and CD56 but not CD20 (figure 1A–E). In situ hybridisation for EBV-encoded mRNA (EBER) was positive in most tumour cells (figure 1F). The patient was transferred to our hospital where CT scans of the neck were negative for lymphadenopathy. There was no tumour in the upper aerodigestive tract by nasopharyngeal scopy. Bone marrow aspiration and biopsy were negative for lymphoma involvement. Under the …