Nasal-type natural killer cell lmyphoma preceded by benign panniculitis arising in an asymptomatic HTLV-1 carrier

We report a case of an Epstein-Barr virus (EBV)-associated nasal-type natural killer cell lymphoma (NKCL) preceded by benign panniculitis, which arose in a 48-year-old woman with an asymptomatic human T-cell leukemia/lymphoma virus type-1 (HTLV-1) infection. A biopsy of the initial panniculitis lesion demonstrated lobular panniculitis with a germinal center composed of benign mononuclear cells with a phehotype of CD4⁺CD45RO⁺CD5sCD3⁺cCD3ε⁺ T-cell intracellular antigen-1 (TIA-1)^- and granzyme B^-. One year after oral prednisolone therapy, the patient developed subcutaneous nodules composed of atypical lymphoid cells with a phenotype of CD4⁺CD45RO⁺CD56⁺sCD3^-cCD3ε ⁺ (TIA-1)⁺ and granzyme B⁺. In the initial panniculitis lesion, neither EBV-encoded RNA (EBER-1) nor clonal proliferation of EBV-infected cells was identified. In later lesions, however, a large number of atypical cells were positive for EBER-1, and a clonal expansion of EBV-infected cells was detected. No clonal rearrangement of T-cell receptor-α, -β, or -γ genes was found in either specimen. This patient was an asymptomatic carrier of human T-cell leukemia/lymphoma virus type-1 (HTLV-1) without clonal integration of proviral HTLV-1 in neither the peripheral blood nor the skin lesions. These observations suggest that EBV-associated NKCL occurred subsequently in the clinical course of benign panniculitis under the influence of immunosuppression caused by prednisolone treatment and HTLV-1 infection.