Tricky and Terrible T-Cell Tumors: These are Thrilling Times for Testing: Molecular Pathology of Peripheral T-Cell Lymphomas

Approach to nodal-based T-cell lymphomas

Peripheral T-cell lymphomas (PTCLs) represent a heterogeneous group of uncommon malignancies derived from mature T cells and usually characterised by an aggressive clinical course. Their clinical presentation, localisation and pattern of dissemination are highly variable, but the majority of cases present as nodal diseases. The recently revised classification of lymphomas has incorporated many new molecular genetic data derived from gene expression profiling and next generation sequencing studies, which refine the definition and diagnostic criteria of several entities. Nevertheless, the distinction of PTCL from various reactive conditions, and the diagnosis of PTCL subtypes remains notably challenging. Here, an updated summary of the clinicopathological and molecular features of the most common nodal-based PTCLs (angioimmunoblastic T-cell lymphoma and other nodal lymphomas derived from follicular T helper cells, anaplastic large cell lymphomas and peripheral T-cell lymphoma, not otherwise specified) is presented. Practical recommendations in the diagnostic approach to nodal T-cell lymphoproliferations are presented, including indications for the appropriate use and interpretation of ancillary studies. Finally, we discuss commonly encountered diagnostic problems, including pitfalls and mimics in the differential diagnosis with various reactive conditions, and the criteria that allow proper identification of distinct PTCL entities.

[Molecular pathogenesis of peripheral T-cell lymphoma (1): angioimmunoblastic T-cell lymphoma, peripheral T-cell lymphoma, not otherwise specified and anaplastic large cell lymphoma]

Peripheral T-cell lymphomas (PTCL) belong to the group of non-Hodgkin lymphoma and particularly that of mature T/NK cells lymphoproliferative neoplasms. The 2008 WHO classification describes different PTCL entities with varying prevalence. With the exception of the histological subtype "ALK positive anaplastic large cell lymphoma", PTCL are characterized by a poor prognosis. The mechanisms underlying the pathogenesis of these lymphomas are not yet fully understood, but development of genomic high-throughput analysis techniques now allows to extensively identify the molecular abnormalities present in tumor cells. This review aims to summarize the current knowledge and recent advances about the molecular events occurring at the origin or during the natural history of main entities of PTCL. It will be published in two parts : the first is focused on the three more frequent entities, angioimmunoblastic T-cell lymphoma, peripheral T-cell lymphoma, not otherwise specified, and anaplastic large cell lymphoma. The second (which will appear in the november issue) will describe other subtypes less frequent and of poor prognosis : extranodal NK/T-cell lymphoma, nasal type, adult T-cell leukemia/lymphoma, and enteropathy-associated T-cell lymphoma. T or NK cell lymphoproliferative disorders with leukemic presentation, primary cutaneous T-cell lymphoma and very rare subtypes of PTCL whose prevalence is less than 5% (hepatosplenic T-cell lymphoma and subcutaneous panniculitis-like T cell lymphoma) will not be discussed herein.

Romidepsin for the Treatment of Peripheral T-Cell Lymphoma

Peripheral T-cell lymphoma (PTCL) is a heterogeneous group of non-Hodgkin lymphomas associated with poor prognosis in most subtypes. Diagnosis of this rare disease by expert hematopathologists improves accuracy of subtyping, and referral to academic or specialty centers is recommended. Many patients, however, will receive treatment in the community, and knowledge of approved agents is key to optimizing therapeutic approaches for all patients. There is no current standard of care for patients with PTCL and no approved therapies for first-line treatment. Although many patients initially respond to induction chemotherapy, responses are often brief, and many patients relapse or become treatment refractory. For patients with relapsed or refractory PTCL, achievement of durable responses is challenging, and there are few treatment options. Romidepsin is a histone deacetylase inhibitor approved by the U.S. Food and Drug Administration for the treatment of patients with cutaneous T-cell lymphoma who have received one prior systemic therapy or more and patients with PTCL who have received one prior therapy or more. Approval of romidepsin for PTCL was based on a pivotal phase II study of patients with relapsed or refractory PTCL (n = 131) that demonstrated an objective response rate of 25% including 15% with complete response; responses lasted a median of >2 years. Long-term responses to romidepsin were achieved in patients regardless of baseline characteristics, including subtype, heavy pretreatment, response to prior therapy, or advanced disease. Common adverse events included hematologic abnormalities, gastrointestinal or asthenic conditions, and infections; romidepsin was not correlated with clinically meaningful QT prolongation or electrocardiogram abnormalities.

IMPLICATIONS FOR PRACTICE

Due to the rarity, severity, and heterogeneous nature of peripheral T-cell lymphoma (PTCL), diagnosis by expert hematopathologists is preferred, and referral to specialty centers is recommended. Many patients, however, will receive treatment in the community, and community oncologists play a key role in the recognition and treatment of PTCL. Knowledge of approved agents is key for optimizing therapeutic approaches. This review provides an overview of PTCL and an in-depth examination of romidepsin, a histone deacetylase inhibitor approved for the treatment of relapsed or refractory PTCL, and highlights difficulties of diagnosis and optimization of treatment modalities for patients with PTCL.