Small-cell predominant extranodal NK/T cell lymphoma, nasal type: clinicopathological analysis of a series of cases diagnosed in a Western population.

AIMS: Extranodal NK/T cell lymphoma, nasal type (ENKTCL) is usually composed of medium- to large-sized lymphoid cells showing prominent angiotrophism and tumour cell necrosis. We report 13 cases composed predominantly of small lymphocytes diagnosed in the United States and Western Europe.

METHODS AND RESULTS: Patients included seven females and six males aged 17-75 years. Ten presented with sinonasal and three with buccal disease. Nine had stage IE/IIE and four had stage IV disease. In five of seven patients with multiple biopsies at different time-intervals, the lymphoma was misinterpreted as representing chronic inflammation on an earlier biopsy. In all cases morphology showed a dense infiltrate of small lymphoid cells with minimal cytological atypia. Necrosis, angioinvasion and angiodestruction were each seen in 17%, 22% and 17% of biopsies. Median Ki67 was 5%. Four patients died of lymphoma 4-16 months after diagnosis, including three of four patients with stage IV disease; seven (54%) are alive with no evidence of disease at a median of 39 months; one patient with stage IV disease is alive at 10 months and one recurred at 17 months.

CONCLUSIONS: In sinonasal biopsies with predominantly small lymphocytic infiltrates with admixed chronic inflammation, focal hypercellularity, focal surface ulceration or microscopic bone invasion by small lymphoid cells should alert pathologists to the possibility of small-cell predominant ENKTCL. Awareness of the full histological spectrum of ENKTCL, particularly in non-endemic areas, is important in avoiding a delay in diagnosis and ensuring timely initiation of therapy.