Geographic Distribution of the Peripheral T‐cell Lymphomas

The T-cell lymphomas are characterized by marked differences in its global patterns of distribution. The epidemiology and classification of non-Hodgkin lymphoma (NHL) has undergone vast transformation over the past few decades. In an attempt to study the geographical distribution of NHL subtypes, the International NHL Classification Project was conducted in the late 1990s. The 2017 WHO classification broadly divides peripheral T-cell lymphomas (PTCL) into three categories based on their location. They are leukemic (disseminated), nodal, and extranodal. These categories are further subdivided based on morphology, immunohistochemistry, and clinical behavior. Examples of these lymphomas include PTCL not otherwise specified (PTCL-NOS), angioimmunoblastic T-cell lymphomas, anaplastic large-cell lymphoma (ALCL), anaplastic lymphoma kinase positive (ALK+), ALK negative (ALK–) ALCL, intestinal T-cell lymphoma, and breast implant-associated ALCL. This chapter discusses the epidemiological data for each of the individual subtype of PTCL.