FoxP3-positive T cell lymphoma arising in non-HTLV1 carrier: Clinicopathological analysis of 11 cases of PTCL-NOS and 2 cases of mycosis fungoides

Aims: Forkhead box protein 3-positive (FoxP3+) T cell lymphoma, in the absence of human T cell lymphotrophic virus type 1 (HTLV-1) infection, is rare and its clinicopathological characteristics still remain unclear. The aim of this study was to elucidate its characteristics. Methods and results: We describe here 11 cases of peripheral T cell lymphoma not otherwise specified (PTCL-NOS) and two cases of mycosis fingoides (MF) which were positive for FoxP3. The median age of the 11 PTCL-NOS cases was 65 years (range: 48-80 years), and all the patients were male. Eight patients (80%) showed stages III/IV disease, and six (60%) were categorized as high-intermediate/high-risk groups according to the International Prognostic Index. Two cases of MF were 57- and 59-year-old males. Both cases were categorized as stage IA, according to International Society for Cutaneous Lymphomas/European Organization of Research and Treatment of Cancer (ISCL/EORTC) classification. Immunohistochemically, all the cases were negative for cytotoxic molecule marker, and nine (75%) were αβ T cell type. Scattered Epstein-Barr virus (EBV)-infected cells were detected in four cases of PTCL-NOS, implying the reactivation of EBV caused by the immunodeficient status of the patients. Conclusions: FoxP3+ PTCL-NOS constitute a minor phenotypical subtype with poor prognosis and EBV reactivation in some. Conversely, two cases of MF showed an indolent clinical course which was different from previously reported cutaneous T cell lymphoma (CTCL) cases.