Primary Cutaneous Extranodal Natural Killer/T-Cell Lymphoma Misdiagnosed as Peripheral T-Cell Lymphoma: The Importance of Consultation/Referral and Inclusion of EBV In Situ Hybridization for Diagnosis.

BACKGROUND: Primary cutaneous T-cell lymphomas (CTCL) are heterogenous extranodal non-Hodgkin lymphomas including a few distinct and provisional entities. Compared with the West, Asian populations have a relatively higher frequency of nonmycosis fungoides CTCL. Primary cutaneous extranodal natural killer/T-cell lymphoma (PC-ENKTL) is distinct from other CTCL by the presence of EBV association. METHOD: In our recent retrospective Asian study of PC-ENKTL, we identified 5 cases initially misdiagnosed as various CTCL. We fully characterized these cases with immunohistochemistry, EBV in situ hybridization, and clonality study for T-cell receptor (TCR) γ-chain gene (TRG). RESULTS: The 5 patients included 3 males and 2 females with a median age of 45. All tumors were positive for EBER. Two cases were clonal for TRG gene rearrangement but without expression of βF1 or TCR-γ (TCR-silent T-cell origin), 1 tumor expressed TCR-γ (γδ T-cell origin), and the remaining 2 were polyclonal for TRG and negative for TCR expression (NK-cell origin). On the basis of the initial diagnoses (2 as peripheral T-cell lymphoma, unspecified, 2 as primary cutaneous anaplastic large-cell lymphoma, and 1 as subcutaneous panniculitis-like T-cell lymphoma), all patients received CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisolone) chemotherapy with additional radiotherapy in 3. All patients experienced persistent disease or relapse despite treatment in a mean duration of 8.8 months (range, 1 to 12 mo). CONCLUSIONS: PC-ENKTL is rare and aggressive. These cases strongly demonstrate the importance of consultation/referral to experienced hematopathologists and the inclusion of EBER in the initial diagnostic work-up for patients with nonmycosis fungoides CTCL to avoid erroneous diagnosis and subsequent inadequate treatment of the patients.