Ferreira CR, et al. - Researchers presented the reports of 6 cases (median age: 56years; male predominance) of T-cell lymphomas with Treg phenotype based on diffuse positivity for Forkhead box P3 (FOXP3) in tumor cells. Lymph nodes (4), skin (2), subcutaneous tissue (1) and bone marrow (1) were the sites involved. They observed monomorphic large cells, some with Hodgkin-like or anaplastic cells in all cases. Pan T cell markers and lack of cytotoxic markers were observed in all cases; one case displayed diffuse PD1 staining. Human T-lymphotrophic virus (HTLV)-1 DNA within tumor cells was noted in one case; this case was classified as adult T-cell leukemia/lymphoma (ATLL). Three were classified as peripheral T-cell lymphoma, not otherwise specified (PTCL, NOS) and 2 fulfilled criteria for ALK-negative anaplastic large cell lymphoma (ALCL) with diffuse and strong CD30 positivity among the 5 HTLV1-negative cases. HTLV1-negative cases, such as PTCL, NOS and ALK-negative ALCL, rarely display Treg phenotype. The findings suggest giving consideration to HTLV1 DNA testing in the appropriate clinical setting to rule out ATLL.