Extranodal natural killer/T-cell lymphoma of the breast: a retrospective clinicopathological analysis of a consecutive 11-year case series.

BACKGROUND Extranodal NK/T-cell lymphoma of the breast (ENKTL-Breast) is rarely detected in clinical practice, and its clinicopathological features remain unclear. RESULTS A consecutive 11-year (2010-2020) ENKTL-Breast case series was retrospectively analyzed. Eight cases of ENKTL-Breast were selected, with three primary and five secondary lesions, accounting for 3.5% (8/228) of all breast lymphomas. All patients were female with a median age of 46 years. Lesions presented as solid breast masses (8/8, 100%) and were usually located in the upper outer quadrant of the breast (7/8, 87.5%). B-symptoms were observed in seven (7/8, 87.5%) cases. Two primary ENKTL-Breast cases showed concomitant diseases (IgA nephropathy and chronic active hepatitis B). Histological and immunohistochemical features of ENKTL-Breast were similar to those of ENKTL at other sites. T-cell receptor rearrangement revealed clonality in all examined primary cases (2/2, 100%), but only in one secondary case (1/5, 20%). The disease progressed rapidly in two primary cases and both patients died within 3 and 9 months. For secondary cases, the disease manifested as a disseminated disease, with a median survival time of 6 months. CONCLUSIONS Our data suggested that ENKTL-Breast clinically mimics breast cancer to some extent, though B-symptoms might serve as a distinguishing factor. ENKTL-Breast is highly aggressive and patients with this disease exhibit a short survival time. Primary ENKTL-Breast tends to originate from activated cytotoxic T-cells, and immune-related diseases may be involved in its pathogenesis and development.