Peripheral T-cell lymphomas (PTCLs) account for about 12% of all lymphoid neoplasms in Western Countries. They show an endemic prevalence in some geographic areas, including southern Japan, Caribbean Basin, and regions of Mexico and USA, where they are related to HTVL1 infection.1 PTCLs can be roughly subdivided into specified and not otherwise specified (NOS) forms (Table 1). While the former correspond to rare but distinct entities, the latter represent about 50% of these tumours. PTCL/NOS is a basket category characterised by great morphologic and phenotypic variability. Due to this, its distinction from angioimmunoblastic T-cell lymphoma (AITL) and anaplastic large cell lymphoma (ALCL) may be difficult based on conventional criteria. Such differential diagnosis is not irrelevant because of potential therapeutic and prognostic implications. In general, the behaviour of PTCLs is aggressive, with the exception of mycosis fungoides (in its early and plaque phases) and primary cutaneous small/medium CD4 positive T-cell lymphoma. Irrespectively of the fact that they have a leukaemic, nodal or extranodal presentation, they show a poor response to current therapies and dismal prognosis, the 5-year overall survival being about 20%.2 Also the usage of supra-maximal approaches has not provided the expected results. This situation probably reflects the limited knowledge on their pathobiology, the interest of most researchers having been focused on the more common B-cell tumours for decades. Only recently, molecular biology studies have opened new scenarios and led to the proposal of novel targeted therapies.