Anaplastic lymphoma kinase proteins and malignancy

The Transcriptional Roles of ALK Fusion Proteins in Tumorigenesis

Anaplastic lymphoma kinase (ALK) is a tyrosine kinase involved in neuronal and gut development. Initially discovered in T cell lymphoma, ALK is frequently affected in diverse cancers by oncogenic translocations. These translocations involve different fusion partners that facilitate multimerisation and autophosphorylation of ALK, resulting in a constitutively active tyrosine kinase with oncogenic potential. ALK fusion proteins are involved in diverse cellular signalling pathways, such as Ras/extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K)/Akt and Janus protein tyrosine kinase (JAK)/STAT. Furthermore, ALK is implicated in epigenetic regulation, including DNA methylation and miRNA expression, and an interaction with nuclear proteins has been described. Through these mechanisms, ALK fusion proteins enable a transcriptional programme that drives the pathogenesis of a range of ALK-related malignancies.

Downregulation of NPM reverses multidrug resistance in human hepatoma cells via inhibition of P-glycoprotein expression

Multidrug resistance (MDR) is an important issue in current cancer treatments. In human cancer, drug resistance is primarily associated with the overexpression of multidrug resistance gene 1 (MDR1). Therefore, the human MDR1 gene promoter may be a target for anti‑MDR drug screening. Numerous methods to prevent MDR have been investigated. However, they have been proven to be clinically ineffective. Therefore, the aim of the present study was to investigate whether downregulation of nucleophosmin (NPM) demonstrates any effects on the reversal of MDR in hepatocellular carcinoma (HCC) cells. In the present study, two in vitro MDR HCC cell lines, HepG2/Adriamycin (ADM) and SMMC7721/ADM, were established and the level of MDR was measured. The results demonstrated that NPM downregulation markedly reversed the effects of MDR in the model used. In addition, NPM downregulation reduced P-glycoprotein expression, as well as MDR1 expression. These results suggested that downregulation of NPM may be a novel and effective method of reversing the effects of MDR, and may be a potential adjuvant for tumor chemotherapy.

Inflammatory myofibroblastic tumour

While initially controversial, the proposal that a subset of inflammatory pseudotumours were myofibroblastic neoplasms is now acknowledged. Inflammatory myofibroblastic tumour is a spindle cell neoplasm of intermediate biological potential that may arise in a wide range of anatomic sites but has a particular propensity for the lung and abdominal soft tissues. Depending on its location, IMT may present with a variety of clinical symptoms and it may also express a variable pathologic phenotype, leading to a broad range of clinical and pathological differentials. Recent discoveries about the molecular signatures of IMT not only provide additional tools to assist in their diagnosis, they also point to possible therapeutic interventions that may transform the management algorithms for patients with this condition.

An inflammatory myofibroblastic tumor exhibiting immunoreactivity to KIT: a case report focusing on a diagnostic pitfall

Inflammatory myofibroblastic tumors (IMTs) and gastrointestinal stromal tumors (GISTs) are both spindle cell tumors, and occur rarely in the wall of the urinary bladder. In general, immunostaining allows differentiation of IMTs and GISTs. Most IMTs are positive for anaplastic lymphoma kinase (ALK) and negative for KIT, whereas most GISTs are ALK-negative and KIT-positive. Here, we describe a case of a spindle cell tumor in the wall of the urinary bladder. The spindle cells were positive for both ALK and KIT, and it was thus difficult to determine whether the tumor was an IMT or a GIST. We eventually diagnosed an IMT, because ALK gene rearrangement was confirmed by fluorescent in-situ hybridization. Cytoplasmic staining for KIT and the absence of other GIST markers, including DOG1 and platelet-derived growth factor α, indicated that the tumor was not a GIST. Therefore, IMTs should be included in the differential diagnosis of spindle cell tumors, even those that are KIT-positive.

ALK Signaling and Target Therapy in Anaplastic Large Cell Lymphoma

The discovery by Morris et al. (1994) of the genes contributing to the t(2;5)(p23;q35) translocation has laid the foundation for a molecular based recognition of anaplastic large cell lymphoma and highlighted the need for a further stratification of T-cell neoplasia. Likewise the detection of anaplastic lymphoma kinase (ALK) genetic lesions among many human cancers has defined unique subsets of cancer patients, providing new opportunities for innovative therapeutic interventions. The objective of this review is to appraise the molecular mechanisms driving ALK-mediated transformation, and to maintain the neoplastic phenotype. The understanding of these events will allow the design and implementation of novel tailored strategies for a well-defined subset of cancer patients.

Anaplastic large-cell lymphoma

The concept of anaplastic large-cell lymphoma (ALCL) has changed over the years because of a stream of new information and novel understanding regarding the cell of origin, biology, genetics, and clinical features of these neoplasms. This new information has led to the current classification proposed by the expert reviewers of the World Health Organization. The objective of this review is to present the most updated information on the cytologic and histologic features of these entities, with a special reference to diagnostic algorithms. A detailed description of the genetic aberrations and the pathogenetic mechanisms leading to transformation is presented. The clinical features of ALCL and novel tailored strategies are briefly illustrated.

Interleukin-9 (IL-9) and NPM-ALK each generate mast cell hyperplasia as single 'hit' and cooperate in producing a mastocytosis-like disease in mice

Mast cell neoplasms are characterized by abnormal growth and focal accumulation of mast cells (MC) in one or more organs. Although several cytokines, including stem cell factor (SCF) and interleukin-9 (IL-9) have been implicated in growth of normal MC, little is known about pro-oncogenic molecules and conditions triggering differentiation and growth of MC far enough to lead to the histopathological picture of overt mastocytosis. The anaplastic lymphoma kinase (ALK) has recently been implicated in growth of neoplastic cells in malignant lymphomas. Here, we describe that transplantation of NPM-ALK-transplanted mouse bone marrow progenitors into lethally irradiated IL-9 transgenic mice not only results in lymphoma-formation, but also in the development of a neoplastic disease exhibiting histopathological features of systemic mastocytosis, including multifocal dense MC-infiltrates, occasionally with devastating growth in visceral organs. Transplantation of NPM-ALK-transduced progenitors into normal mice or maintenance of IL-9-transgenic mice without NPM-ALK each resulted in MC hyperplasia, but not in mastocytosis. Neoplastic MC in mice not only displayed IL-9, but also the IL-9 receptor, and the same was found to hold true for human neoplastic MC. Together, our data show that neoplastic MC express IL-9 receptors, that IL-9 and NPM-ALK upregulate MC-production in vivo, and that both'hits' act in concert to induce a mastocytosis-like disease in mice. These data may have pathogenetic and clinical implications and fit well with the observation that neoplastic MC in advanced SM strongly express NPM and multiple "lymphoid" antigens including CD25 and CD30.

Guidelines for the management of mature T-cell and NK-cell neoplasms (excluding cutaneous T-cell lymphoma)

The peripheral T-cell neoplasms are a biologically and clinically heterogeneous group of rare disorders that result from clonal proliferation of mature post-thymic lymphocytes. Natural killer (NK) cell neoplasms are included in this group. The World Health Organization classification of haemopoietic malignancies has divided this group of disorders into those with predominantly leukaemic (disseminated), nodal, extra-nodal or cutaneous presentation. They usually affect adults and are more commonly reported in males than in females. The median age at diagnosis is 61 years with a range of 17-90 years. Although some subtypes may follow a relatively benign protracted course most have an aggressive clinical behaviour and poor prognosis. Excluding anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL), which has a good outcome, 5-year survival for other nodal and extranodal T-cell lymphomas is about 30%. Most patients present with unfavourable international prognostic index scores (>3) and poor performance status. The rarity of these diseases and the lack of randomized trials mean that there is no consensus about optimal therapy for T- and NK-cell neoplasms and recommendations in this guideline are therefore based on small case series, phase II trials and expert opinion.

Interleukin-9 (IL-9) and NPM-ALK each generate mast cell hyperplasia as single 'hit' and cooperate in producing a mastocytosis-like disease in mice

Mast cell neoplasms are characterized by abnormal growth and focal accumulation of mast cells (MC) in one or more organs. Although several cytokines, including stem cell factor (SCF) and interleukin-9 (IL-9) have been implicated in growth of normal MC, little is known about pro-oncogenic molecules and conditions triggering differentiation and growth of MC far enough to lead to the histopathological picture of overt mastocytosis. The anaplastic lymphoma kinase (ALK) has recently been implicated in growth of neoplastic cells in malignant lymphomas. Here, we describe that transplantation of NPM-ALK-transplanted mouse bone marrow progenitors into lethally irradiated IL-9 transgenic mice not only results in lymphoma-formation, but also in the development of a neoplastic disease exhibiting histopathological features of systemic mastocytosis, including multifocal dense MC-infiltrates, occasionally with devastating growth in visceral organs. Transplantation of NPM-ALK-transduced progenitors into normal mice or maintenance of IL-9-transgenic mice without NPM-ALK each resulted in MC hyperplasia, but not in mastocytosis. Neoplastic MC in mice not only displayed IL-9, but also the IL-9 receptor, and the same was found to hold true for human neoplastic MC. Together, our data show that neoplastic MC express IL-9 receptors, that IL-9 and NPM-ALK upregulate MC-production in vivo, and that both'hits' act in concert to induce a mastocytosis-like disease in mice. These data may have pathogenetic and clinical implications and fit well with the observation that neoplastic MC in advanced SM strongly express NPM and multiple "lymphoid" antigens including CD25 and CD30.

Posttransplant Epstein-Barr virus-associated myogenic tumors: case report and review of the literature

Epstein-Barr virus (EBV) has been implicated in the pathogenesis of different types of malignancies. While nonmelanoma skin cancers, lymphomas and Kaposi sarcomas are the most frequently reported malignancies after solid organ transplantation, EBV-associated smooth muscle tumors (EBV-SMT) after transplantation are rare and thus far only 18 cases in kidney recipients have been reported. A case of a 51-year-old kidney transplant recipient diagnosed with EBV-SMT is reported together with a review of the literature.

Human γδ T lymphocytes strip and kill tumor cells simultaneously

When human gammadelta lymphocytes bind to tumor cells for killing, they also strip their membrane for unknown reasons. Here we investigated this topic using the model of human gammadelta lymphocytes co-incubated with anaplastic large cell lymphomas, a group of tumors with cytolytic T or null lineage. By using flow cytometry and live cell imaging, we show that as soon as both cells were in contact, the TCR-mediated activation of gammadelta lymphocytes simultaneously triggered their secretion of lytic granules and stripping of lymphoma cell membranes, and both activities continued even after their cell death. However reciprocally in such conjugates, resistant lymphoma failed to strip gammadelta cells and to kill them by untargeted secretion of their own lytic granules. This indicated that secretion of lytic granules and target membrane stripping are associated in lytic cell conjugates, and that gammadelta T lymphocytes strip and kill their targets simultaneously.

TPM3-ALK expression induces changes in cytoskeleton organisation and confers higher metastatic capacities than other ALK fusion proteins

Translocations of the anaplastic lymphoma kinase (ALK) gene result in the production of a number of oncogenic ALK fusion proteins implicated in tumour development. We have previously shown that X-ALK fusion proteins have differential effects on the proliferation, transformation, and invasion properties of NIH3T3 cells in vitro. In the present study, we have investigated the metastatic potential of various X-ALK expressing cell lines using an experimental lung metastasis assay. We have shown that TPM3-ALK expression bestows higher metastatic capacities than other X-ALK fusion proteins and in addition, that TPM3-ALK fusion protein expression specifically induces changes in cell morphology and cytoskeleton organisation. Co-immunoprecipitation studies demonstrate a specific interaction between TPM3-ALK and endogenous tropomyosin. Together the specific actions of TPM3-ALK on the cytoskeleton organisation offer an interesting hypothesis with respect to the higher cell motility and metastatic potential of this fusion protein.

Increased expression of nucleophosmin/B23 in hepatocellular carcinoma and correlation with clinicopathological parameters

Nucleophosmin (NPM, B23, numatrin, NO38) is an abundant nucleolar phosphoprotein involved in multiple cellular functions. Previous evidence indicates that high-level expression of NPM causes uncontrolled cell growth and suggests that NPM may have oncogenic potential. In this study, we examined NPM expression in 103 paired cases of hepatocellular carcinoma (HCC), 12 cases of hepatic focal nodular hyperplasia, 17 cases of liver tissue adjacent to a hepatic haemangioma, and series of array tissues from normal human organs and malignancies using a monoclonal antibody against NPM and reverse transcription-PCR techniques, Western blot analysis, immunohistochemistry, and immunocytofluorescence. Our data indicated that NPM expression was significantly higher in HCC than in the non-malignant hepatocytes (P<0.001). Nucleophosmin was weakly expressed in hepatocytes from a 5-month-old embryo and in stationary hepatocytes of healthy adults. Moreover, enhanced expression of NPM in HCC correlated with the level of PCNA (R(2)=0.5639) and with the clinical prognostic parameters such as serum alpha fetal protein level, tumour pathological grading, and liver cirrhosis (P<0.05). Our results suggest that NPM may play an important role in the progression of tumorigenesis and that NPM may serve as a potential marker for HCC.

Identification of NVP-TAE684, a potent, selective, and efficacious inhibitor of NPM-ALK

Constitutive overexpression and activation of NPM-ALK fusion protein [t(2:5)(p23;q35)] is a key oncogenic event that drives the survival and proliferation of anaplastic large-cell lymphomas (ALCLs). We have identified a highly potent and selective small-molecule ALK inhibitor, NVP-TAE684, which blocked the growth of ALCL-derived and ALK-dependent cell lines with IC(50) values between 2 and 10 nM. NVP-TAE684 treatment resulted in a rapid and sustained inhibition of phosphorylation of NPM-ALK and its downstream effectors and subsequent induction of apoptosis and cell cycle arrest. In vivo, NVP-TAE684 suppressed lymphomagenesis in two independent models of ALK-positive ALCL and induced regression of established Karpas-299 lymphomas. NVP-TAE684 also induced down-regulation of CD30 expression, suggesting that CD30 may be used as a biomarker of therapeutic NPM-ALK kinase activity inhibition.

In situ detection of hTERT variants in anaplastic large cell lymphoma

The expression of hTERT and its isoforms is difficult to assess in lymphoma tissues with the commonly used reverse transcription-polymerase chain reaction (RT-PCR) methods, because non-neoplastic lymphocytes expressing hTERT are always present in the lymphomatous infiltrates. The present study aimed to investigate hTERT mRNA variants in anaplastic large cell lymphoma (ALCL) (n = 38) with in situ hybridization (ISH), along with the immunodetection of hTERT protein. Probes for the identification of mRNAs containing (Bplus) and lacking (Bdel) exons 7 and 8 of the hTERT mRNA were used. Normal lymphocyte populations equally expressed both Bplus and Bdel mRNAs. Although all ALCL examined were found positive for hTERT expression with RT-PCR, hTERT mRNAs were identified in 68% of these tumors with ISH, with a higher incidence in the group bearing ALK translocations (10 out of 11; 90.9%) compared to the ALK negative group (17 out of 27; 59.3%) (PPearson's = 0.002). The same results were obtained with immunohistochemistry for hTERT. In approximately 50% of cases, only Bplus positive cells were identified, again with a higher incidence in the ALK positive compared to the ALK negative group (PPearson's = 0.016). In conclusion, ISH for hTERT mRNAs appears to be a valuable tool for the investigation of hTERT expression in lymphomas. Aberrations in hTERT variant profiles and a decline in the expression of the B deleted isoform may be associated with the pathogenesis of ALCL, especially with respect to ALK positive tumors.

Proteomic identification of oncogenic chromosomal translocation partners encoding chimeric anaplastic lymphoma kinase fusion proteins

The anaplastic lymphoma kinase (ALK) on 2p23 is a tyrosine kinase that forms chimeric fusions with numerous translocation partners. We describe a mass spectrometry-based approach for the identification of ALK fusion partners. This approach accurately identified the nucleophosmin (NPM)-ALK fusion protein in an anaplastic large cell lymphoma (ALCL)-derived cell line carrying the t(2;5)(p23;q35), and the TPM3-ALK in a clinical biopsy of inflammatory myofibroblastic tumor (IMT) carrying the t(1;2)(q21;p23). This study shows the ability of mass spectrometry to identify oncogenic chimeric proteins resulting from chromosomal rearrangements. This strategy can be adapted for the identification of known and unknown translocation partners of chimeric ALK fusion proteins involved in oncogenesis.

SHP1 tyrosine phosphatase negatively regulates NPM-ALK tyrosine kinase signaling

Anaplastic large-cell lymphoma (ALCL) is frequently associated with the 2;5 translocation and expresses the NPM-ALK fusion protein, which possesses a constitutive tyrosine kinase activity. We analyzed SHP1 tyrosine phosphatase expression and activity in 3 ALK-positive ALCL cell lines (Karpas 299, Cost, and SU-DHL1) and in lymph node biopsies (n = 40). We found an inverse correlation between the level of NPM-ALK phosphorylation and SHP1 phosphatase activity. Pull-down and coimmunoprecipitation experiments demonstrated a SHP1/NPM-ALK association. Furthermore, confocal microscopy performed on ALCL cell lines and biopsy specimens showed the colocalization of the 2 proteins in cytoplasmic bodies containing Y664-phosphorylated NPM-ALK. Dephosphorylation of NPM-ALK by SHP1 demonstrated that NPM-ALK was a SHP1 substrate. Downregulation of SHP1 expression by RNAi in Karpas cells led to hyperphosphorylation of NPM-ALK, STAT3 activation, and increase in cell proliferation. Furthermore, SHP1 overexpression in 3T3 fibroblasts stably expressing NPM-ALK led to the decrease of NPM-ALK phosphorylation, lower cell proliferation, and tumor progression in nude mice. These findings show that SHP1 is a negative regulator of NPM-ALK signaling. The use of tissue microarrays revealed that 50% of ALK-positive ALCLs were positive for SHP1. Our results suggest that SHP1 could be a critical enzyme in ALCL biology and a potential therapeutic target.

ALK positive inflammatory myofibroblastic tumour of the pineal region

Inflammatory myofibroblastic tumours (IMTs) are an uncommon spindle cell neoplasm with a dense inflammatory infiltrate, usually encountered in children. IMTs of the central nervous system are extremely rare. This report describes the case of an IMT in a 61 year old man, in the pineal region. The tumour was completely excised, and immunohistochemistry demonstrated anaplastic lymphoma kinase 1 expression. There was no tumour recurrence during 18 months of follow-up. Our case extends both the age range and sites of occurrence of this rare tumour.

Pediatric inflammatory myofibroblastic tumor: anaplastic lymphoma kinase (ALK) expression and prognosis

BACKGROUND

Pediatric inflammatory myofibroblastic tumor (IMT) is rare, with unpredictable clinical behavior. Recently, it has been associated with anaplastic lymphoma kinase (ALK) expression.

METHODS

Patients under age 16, treated for IMT between 1976 and 2000 were reviewed. Mean follow-up was 8 years (range 1 month-22 years).

RESULTS

Eight children had IMT, with a mean age of 6 years (range, 11 months-14 years) and female to male ratio of 3:1. Tumor location was lung (four patients), abdomen (two patients), lung and abdomen (one patient), and abdomen, head, and neck (one patient). Presenting symptoms included anemia (seven patients), fever (six patients), and dyspnea (four patients). Laboratory results included thrombocytosis (six patients), hypergammaglobulinemia (four patients), elevated sedimentation rate (four patients), and leukocytosis (three patients). Immunohistochemistry revealed ALK expression in four of eight tumors. Four children had complete resection and are alive. Two of these children had ALK-positive tumors. Four patients had incomplete resection, and two had recurrences treated successfully with resection and radiotherapy; the other two died of disease. For the incomplete resection patients, those that were ALK-positive lived, and those that were ALK-negative did not.

CONCLUSIONS

Eight children were treated for IMT over a 15-year period. ALK expression was found in half the tumors. Prognosis was improved with ALK expression and complete surgical resection.

Childhood and adolescent non-Hodgkin lymphoma: new insights in biology and critical challenges for the future

Pediatric non-Hodgkin lymphoma (NHL) is a common and fascinating group of diseases with distinctive underlying genetic events that characterize the major histologic subtypes: diffuse large B-cell lymphoma, Burkitt lymphoma, anaplastic large cell lymphoma and lymphoblastic lymphoma. With systematic improvements in therapy over recent decades, the vast majority of children with NHL of all subtypes are now cured. The similarities and differences between adult and childhood presentations of disease, and whether or not some subtypes of NHL and leukemia are the same or different disease entities, are interesting questions that will be addressed with advances in our understanding of the molecular and genetic bases of these diseases. As is the case with other pediatric malignancies, growing emphasis is now being placed on the development of less toxic, targeted therapeutic approaches, and this review highlights some of the biological discoveries that will potentially open these avenues.

Inhibition of JAK3 induces apoptosis and decreases anaplastic lymphoma kinase activity in anaplastic large cell lymphoma

Signal transducer and activator of transcription 3 (STAT3), normally activated by Janus kinase (JAK) in response to cytokine stimulation, has been shown to have oncogenic potential. In addition to JAK, recent data suggest that STAT3 can also be activated by other proteins such as the aberrant fusion protein, NPM-ALK, which is expressed in a subset of systemic anaplastic large cell lymphoma (ALCL). In this study, we investigated the possible role of JAK in activating STAT3 in ALCL using two ALK-positive ALCL cell lines, Karpas 299 and SU-DHL-1. At the steady state, JAK3 showed detectable tyrosine phosphorylation by immunoprecipitation. Treatment with AG490, a JAK inhibitor, decreased but did not completely abrogate tyrosine phosphorylation of JAK3 and STAT3 in a concentration-dependent manner. Similar results were obtained using two other inhibitors of JAK3, WHI-P131 and WHI-P154. These biochemical changes were associated with apoptosis in both cell lines that was coupled with activation of caspase 3 and decreased bcl-xL and bcl-2. Cell cycle analysis revealed a decrease in the S phase, which may be attributed to cyclin D3 downregulation and p21(waf1) upregulation. Importantly, the tyrosine kinase activity of NPM-ALK, as assessed by an in vitro assay, decreased with increasing concentrations of AG490. Our findings highlight the importance of JAK3 in activating STAT3 in ALCL, and that NPM-ALK-mediated activation of STAT3 is influenced by the functional status of JAK3.

Primary anaplastic large cell lymphoma of the central nervous system: prognostic effect of ALK-1 expression

Anaplastic large cell lymphoma (ALCL) rarely occurs in the central nervous system. Although defined by its composition of large, pleomorphic, CD30-positive lymphocytes, ALCL is heterogeneous. Most are T cell but some are null cell. Most but not all have a characteristic 2:5 translocation producing the fusion protein ALK-1, which is reliably detected by immunohistochemistry. In systemic ALCL, ALK-1 expression correlates with young patient age and a favorable prognosis. Herein we report four new cases of primary central nervous system ALCL from the Mayo Clinic and incorporate additional data from five previously published cases. ALK-1 expression was determined in all nine tumors. Patient age was 4-66 years (mean 29 years) with a bimodal distribution: 6 < or = 22 years, 3 > or = 50 years. Six were female. Tumors were mostly supratentorial, five were multifocal, and seven had involvement of dura or leptomeninges. Seven tumors were T cell, two were null cell, and five of nine were ALK-1 immunopositive. Total mortality was six of nine. Three patients, 4-18 years of age (mean 13 years), were alive at 4.8-6.1 years postdiagnosis; these tumors were all ALK positive. Five patients, 13-66 years of age (mean 43 years), died of tumor 4 days to 11 weeks postdiagnosis; four of five of these tumors were ALK negative. One 10-year-old child with an ALK-positive tumor died of sepsis, but in remission. Central nervous system ALCL is aggressive. Our study suggests that a better outcome may be associated with young age and ALK-1 positivity, prognostic parameters similar to systemic ALCL.

Molecular biology of anaplastic lymphoma kinase-positive anaplastic large-cell lymphoma

Anaplastic large-cell lymphoma (ALCL) provides an excellent example of how molecular insights into tumor pathogenesis are influencing and improving tumor classification. ALCL was described initially as a subtype of T-cell/null-cell lymphoma characterized by unusual tumor cell morphology and the expression of CD30. However, it was soon recognized that a subset of ALCLs contained chromosomal translocations involving anaplastic lymphoma kinase (ALK), a novel receptor tyrosine kinase gene. These rearrangements create chimeric genes encoding self-associating, constitutively active ALK fusion proteins that activate a number of downstream effectors, including phospholipase C-gamma, phosphoinositol 3'-kinase, RAS, and signal transducer and activator of transcription proteins, all of which seem potentially important in cellular transformation. Not all tumors classified as ALCLs have ALK rearrangements and, conversely, ALK rearrangements occur in lymphomas of widely varying morphology. Hence, only molecular markers can reliably identify ALK+ ALCL. The importance of doing so is reflected by clinical studies suggesting that ALK+ ALCLs have a significantly better prognosis than other aggressive peripheral T-cell or B-cell lymphomas, including ALK- ALCLs. The unique molecular pathogenesis of ALK+ ALCL is likely to lead to novel therapeutic approaches directed at specific inhibition of ALK or downstream effectors.