T-cell non-Hodgkin's lymphomas (NHL) are uncommon malignancies, representing approximately 12% of all lymphomas. Various geographic frequencies of T-cell NHL have been documented, ranging from 18.3% of NHL diagnosed in Hong Kong to 1.5% in Vancouver, Canada. This may in part reflect increased exposure to pathogenic factors such as human T-cell leukemia virus 1 (HTLV-1) and Epstein–Barr virus (EBV) in Asian nations. T-cell NHL commonly presents with extranodal disease and often contains varying amounts of necrosis/apoptosis on biopsy specimens, making differentiation between a reactive process and lymphoma challenging. Immunophenotypic, cytogenetic and molecular analyses have enhanced diagnostic capabilities as well as improved classification and prognostication for T-cell NHL.
The current World Health Organization/European Organisation for Research and Treatment of Cancer (WHO/EORTC) classification recognizes nine distinct clinicopathologic peripheral T-cell NHLs. The broad spectrum of pathologic subtypes with varied clinical behavior poses a challenge to the systematic study of these diseases. Furthermore, these distinct T-cell NHL subtypes have unique characteristics and often warrant individualized diagnostic and therapeutic treatment strategies. The primary cutaneous T-cell lymphomas are reviewed in Chapter 16. Here we review the etiology, pathology, diagnosis and treatment strategies for patients with peripheral T-cell lymphomas (Table 15.1).
Genetic alterations involved in lymphoma oncogenesis include chromosome rearrangements, disruption of tumor suppressor genes and an increase in the number of copies of genes (gene amplification). Moreover, infection of cells by viruses and bacteria such as HTLV-I, human herpesvirus 8 (HHV-8), hepatitis C and Helicobacter pylori may also contribute to lymphomagenesis.