• Diagnostic signatures for PTCL subtypes and 2 novel subgroups with distinct oncogenic pathway and prognostic importance in PTCL-NOS were identified. • Demonstrated that ALK(-) ALCL is a distinct molecular entity and the tumor microenvironment has prognostic significance in AITL patients.Peripheral T-cell lymphoma (PTCL) encompasses a heterogeneous group of neoplasms with generally poor clinical outcome. Currently 50% of PTCL cases are not classifiable: PTCL-not otherwise specified (NOS). Gene-expression profiles on 372 PTCL cases were analyzed and robust molecular classifiers and oncogenic pathways that reflect the pathobiology of tumor cells and their microenvironment were identified for major PTCL-entities, including 114 angioimmunoblastic T-cell lymphoma (AITL), 31 anaplastic lymphoma kinase (ALK)-positive and 48 ALK-negative anaplastic large cell lymphoma, 14 adult T-cell leukemia/lymphoma and 44 extranodal NK/T-cell lymphoma that were further separated into NK-cell and gdT-cell lymphomas. Thirty-seven percent of morphologically diagnosed PTCL-NOS cases were reclassified into other specific subtypes by molecular signatures. Reexamination, immunohistochemistry, and IDH2 mutation analysis in reclassified cases supported the validity of the reclassification. Two major molecular subgroups can be identified in the remaining PTCL-NOS cases characterized by high expression of either GATA3 (33%; 40/121) or TBX21 (49%; 59/121). The GATA3 subgroup was significantly associated with poor overall survival (P 5 .01). High expression of cytotoxic genesignature within the TBX21 subgroup also showed poor clinical outcome (P 5 .05). In AITL, high expression of several signatures associated with the tumor microenvironment was significantly associated with outcome. A combined prognostic score was predictive of survival in an independent cohort (P 5

The tumor microenvironment plays an important role in the biologic behavior of follicular lymphoma (FL), but the specific cell subsets involved in this regulation are unknown. To determine the impact of FOXP3-positive regulatory T cells (Tregs) in the progression and outcome of FL patients, we examined samples from 97 patients at diagnosis and 37 at first relapse with an anti-FOXP3 monoclonal antibody. Tregs were quantified using computerized image analysis. The median overall survival (OS) of the series was 9.9 years, and the FL International Prognostic Index (FLIPI) was prognostically significant. The median Treg percentage at diagnosis was 10.5%. Overall, 49 patients had more than 10% Tregs, 30 between 5% to 10%, and 19 less than 5%, with a 5-year OS of 80%, 74%, and 50%, respectively (P ‫؍‬ .001). Patients with very low numbers of Tregs (< 5%) presented more frequently with refractory disease (P ‫؍‬ .007). The prognostic significance of Treg numbers was independent of the FLIPI. Seven transformed diffuse large B-cell lymphomas (DLBCLs) had lower Treg percentages (mean: 3.3%) than FL grades 1,2 (mean: 12.1%) or 3 (mean: 9%) (P < .02).