Biochemical detection of novel anaplastic lymphoma kinase proteins in tissue sections of anaplastic large cell lymphoma

Molecular Screening in Anaplastic Lymphoma Kinase-Positive Anaplastic Large Cell Lymphoma: Anaplastic Lymphoma Kinase Analysis, Next-Generation Sequencing Fusion Gene Detection, and T-Cell Receptor Immunoprofiling

Anaplastic lymphoma kinase-positive anaplastic large cell lymphoma (ALK+ ALCL) originates from the T-lineage and is marked by rearrangements of the ALK gene. More than 10 fusion partners with the ALK gene are known, with the most common being the t(2;5)(p23;q35) translocation resulting in the NPM1::ALK fusion. In 10% to 20% of the ALK+ ALCL cases, the ALK gene fuses with various other partners. Modern molecular techniques, especially next-generation sequencing (NGS), have eased the identification of ALK gene fusion partners and have allowed in-depth characterization of the T-cell receptor (TCR) repertoire. We devised a real-time quantitative reverse-transcription polymerase chain reaction to measure the expression of the translocated portion of the ALK gene. Fusion partners for the ALK gene were analyzed using rapid amplification of 5'cDNA ends (RACE) method or NGS. TCR immunoprofiling was performed by amplicon NGS. We studied 96 ALK+ ALCL patients. NPM1::ALK fusion gene was observed in 71 patients, ATIC::ALK in 9, and TPM3::ALK in 3. CLTC::ALK, MYH9::ALK, and RNF213::ALK fusions were identified in 2 patients each. We also discovered the TPM4::ALK and SATB1::ALK fusion genes, plus the following 2 previously unidentified ALK+ ALCL fusions: SQSTM1::ALK and CAPRIN1::ALK. High expression of the translocated ALK gene segment was observed in all 93 analyzed samples. TCR testing was conducted on 23 patients with available DNA. In 18 (78%) patients, we discerned at least one (ranging from 1 to 4) clonal TCR rearrangement. In 59% of the patients, clonal TCR beta junctions corresponded with sequences previously observed in both healthy donors and under various pathological conditions. Reverse-transcriptase quantitative detection of ALK expression is a fast and reliable method for both diagnosing and monitoring treatment response in ALK+ ALCL patients, irrespective of the ALK gene translocation. NGS reveals new ALK translocation partners. Both malignant and reactive TCR repertoires in ALK+ ALCL patients are unique and do not consistently occur among different patients.

Recombinant expression, characterization, and quantification in human cancer cell lines of the Anaplastic Large-Cell Lymphoma-characteristic NPM-ALK fusion protein

Systemic anaplastic large cell lymphoma (ALCL) is an aggressive T-cell lymphoma most commonly seen in children and young adults. The majority of pediatric ALCLs are associated with the t(2;5)(p23;q35) translocation which fuses the Anaplastic Lymphoma Kinase (ALK) gene with the Nucleophosmin (NPM) gene. The NPM-ALK fusion protein is a constitutively-active tyrosine kinase, and plays a major role in tumor pathogenesis. In an effort to advance novel diagnostic approaches and the understanding of the function of this fusion protein in cancer cells, we expressed in E. coli, purified and characterized human NPM-ALK fusion protein to be used as a standard for estimating expression levels in cultured human ALCL cells, a key tool in ALCL pathobiology research. We estimated that NPM-ALK fusion protein is expressed at substantial levels in both Karpas 299 and SU-DHL-1 cells (ca. 4-6 million molecules or 0.5-0.7 pg protein per cell; based on our in-house developed NPM-ALK ELISA; LOD of 40 pM) as compared to the ubiquitous β-actin protein (ca. 64 million molecules or 4.5 pg per lymphocyte). We also compared NPM-ALK/ β-actin ratios determined by ELISA to those independently determined by two-dimensional electrophoresis and showed that the two methods are in good agreement.

ALK-positive (2p23 rearranged) anaplastic large cell lymphoma with localization to the skin in a pediatric patient

Anaplastic large cell lymphoma (ALCL) either as primary cutaneous or nodal disease is rare in children and difficult to distinguish, which is important both prognostically and for treatment purposes. We present a case of anaplastic lymphoma kinase (ALK)+ skin-limited ALCL that highlights this challenge and draws attention to pitfalls in assessing ALK status. The patient was an 11-year old girl with a twice recurrent nodule on her right shoulder. Each biopsy revealed a deep infiltrate of atypical lymphocytes that expressed CD3, CD4, CD43, CD45RO and CD30. The initial biopsy was epithelial membrane antigen (EMA)+ with vague cytoplasmic ALK-1 positivity by immunohistochemistry, while the second biopsy was EMA+ and nuclear ALK-1+. Fluorescence in situ hybridization analysis for an ALK (2p23) rearrangement of the first specimen was negative, while an ALK gene rearrangement was present in the second specimen. Therefore, this case was treated as nodal ALCL, despite negative bone marrow and radiographic imaging studies. The patient was treated with combination chemotherapy and remains disease-free. Demonstration of nuclear ALK-positivity, ALK (2p23) gene rearrangement is suggestive of systemic ALCL. Without evidence of systemic disease, this case highlights challenges of skin-limited ALCL, whose clinical behavior as either cutaneous ALCL systemic ALCL may not be immediately apparent.

The EML4-ALK transcript but not the fusion protein can be expressed in reactive and neoplastic lymphoid tissues

Rearrangements involving the ALK gene define two distinct entities in the new 2008 WHO classification of lymphoid neoplasms, i.e. ALK+ anaplastic large cell lymphoma and a rare subset of ALK+ diffuse large B-cell lymphoma. Recently, rearrangements involving ALK and the echinoderm microtubule associated protein-like 4 (EML4) gene were described as a specific genetic alteration in about 6% of non-small cell lung cancer (NSCLC). We investigated the expression of EML4-ALK mRNA and protein in 51 reactive and 58 neoplastic lymphoid tissues. EML4-ALK transcripts were detected in 3/51 (5.9%) of reactive lymphoid tissues and 12/58 (20.7%) of lymphomas of different categories, including follicular lymphoma, diffuse large B-cell lymphoma and Hodgkin's disease. Notably, none of these cases expressed the EML4-ALK fusion protein at Western blotting samples and immunohistochemistry. These results indicate that EML4-ALK rearrangements are not specific of NSCLC and raise yet unsolved questions about their role in promoting human neoplasms.

Anaplastic lymphoma kinase: role in cancer pathogenesis and small-molecule inhibitor development for therapy

Anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase in the insulin receptor superfamily, was initially identified in constitutively activated oncogenic fusion forms - the most common being nucleophosmin-ALK - in anaplastic large-cell lymphomas, and subsequent studies have identified ALK fusions in diffuse large B-cell lymphomas, systemic histiocytosis, inflammatory myofibroblastic tumors, esophageal squamous cell carcinomas and non-small-cell lung carcinomas. More recently, genomic DNA amplification and protein overexpression, as well as activating point mutations, of ALK have been described in neuroblastomas. In addition to those cancers for which a causative role for aberrant ALK activity is well validated, more circumstantial links implicate the full-length, normal ALK receptor in the genesis of other malignancies - including glioblastoma and breast cancer - via a mechanism of receptor activation involving autocrine and/or paracrine growth loops with the reported ALK ligands, pleiotrophin and midkine. This review summarizes normal ALK biology, the confirmed and putative roles of ALK in the development of human cancers and efforts to target ALK using small-molecule kinase inhibitors.

EML4-ALK rearrangement in non-small cell lung cancer and non-tumor lung tissues

A fusion gene, echinoderm microtubule associated protein like 4-anaplastic lymphoma kinase (EML4-ALK), with transforming activity has recently been identified in a subset of non-small cell lung cancer (NSCLC), but its pathogenetic, diagnostic, and therapeutic roles remain unclear. Both frequency and type of EML4-ALK transcripts were investigated by reverse transcription PCR in 120 frozen NSCLC specimens from Italy and Spain; non-neoplastic lung tissues taken far from the tumor were used as controls. In cases carrying the fusion transcript, we determined EML4-ALK gene and protein levels using fluorescence in situ hybridization, Western blotting, and immunoprecipitation. We also analyzed ALK protein levels in paraffin samples from 662 NSCLC specimens, including the 120 cases investigated in the molecular studies. EML4-ALK transcripts (variants 1 and 3) were detected in 9 of 120 NSCLC samples but were not specific for NSCLC since they were also found in non-cancerous lung tissues taken far from the tumor. Notably, no transcripts were detected in matching tumor samples from these patients. Fluorescence in situ hybridization analysis of cases expressing EML4-ALK transcripts showed that only a minority of cells harbored the EML4-ALK gene. None of these cases was found to express the EML4-ALK protein as examined by immunohistochemistry, Western blotting, and immunoprecipitation. The EML4-ALK transcript cannot be regarded as a specific diagnostic tool for NSCLC. Our results show therefore that the causal role and value of EML4-ALK as a therapeutic target remain to be defined.

Development of anaplastic lymphoma kinase (ALK) small-molecule inhibitors for cancer therapy

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) involved in the genesis of several human cancers; indeed, ALK was initially identified in constitutively activated and oncogenic fusion forms--the most common being nucleophosmin (NPM)-ALK--in a non-Hodgkin's lymphoma (NHL) known as anaplastic large-cell lymphoma (ALCL) and subsequent studies identified ALK fusions in the human sarcomas called inflammatory myofibroblastic tumors (IMTs). In addition, two recent reports have suggested that the ALK fusion, TPM4-ALK, may be involved in the genesis of a subset of esophageal squamous cell carcinomas. While the cause-effect relationship between ALK fusions and malignancies such as ALCL and IMT is very well established, more circumstantial links implicate the involvement of the full-length, normal ALK receptor in the genesis of additional malignancies including glioblastoma, neuroblastoma, breast cancer, and others; in these instances, ALK is believed to foster tumorigenesis following activation by autocrine and/or paracrine growth loops involving the reported ALK ligands, pleiotrophin (PTN) and midkine (MK). There are no currently available ALK small-molecule inhibitors approved for clinical cancer therapy; however, recognition of the variety of malignancies in which ALK may play a causative role has recently begun to prompt developmental efforts in this area. This review provides a succinct summary of normal ALK biology, the confirmed and putative roles of ALK fusions and the full-length ALK receptor in the development of human cancers, and efforts to target ALK using small-molecule kinase inhibitors.

The oncoprotein NPM-ALK of anaplastic large-cell lymphoma induces JUNB transcription via ERK1/2 and JunB translation via mTOR signaling

Anaplastic large cell lymphomas (ALCLs) are highly proliferating tumors that commonly express the AP-1 transcription factor JunB. ALK fusions occur in approximately 50% of ALCLs, and among these, 80% have the t(2;5) translocation with NPM-ALK expression. We report greater activity of JunB in NPM-ALK-positive than in NPM-ALK-negative ALCLs. Specific knockdown of JUNB mRNA using small interfering RNA and small hairpin RNA in NPM-ALK-expressing cells decreases cellular proliferation as evidenced by a reduced cell count in the G2/M phase of the cell cycle. Expression of NPM-ALK results in ERK1/2 activation and transcriptional up-regulation of JUNB. Both NPM-ALK-positive and -negative ALCL tumors demonstrate active ERK1/2 signaling. In contrast to NPM-ALK-negative ALCL, the mTOR pathway is active in NPM-ALK-positive lymphomas. Pharmacological inhibition of mTOR in NPM-ALK-positive cells down-regulates JunB protein levels by shifting JUNB mRNA translation from large polysomes to monosomes and ribonucleic particles (RNPs), and decreases cellular proliferation. Thus, JunB is a critical target of mTOR and is translationally regulated in NPM-ALK-positive lymphomas. This is the first study demonstrating translational control of AP-1 transcription factors in human neoplasia. In conjunction with NPM-ALK, JunB enhances cell cycle progression and may therefore represent a therapeutic target.

Highly aggressive ALK-positive anaplastic large cell lymphoma with a leukemic phase and multi-organ involvement: a report of three cases and a review of the literature

Anaplastic large cell lymphoma (ALCL) is an aggressive neoplasm of T- or null cell phenotype and is recognized as a distinct clinicopathologic subtype of non-Hodgkin lymphoma (NHL) in the revised World Health Organization (WHO) classification of hematopoietic neoplasms. It is rarely associated with leukemic phase. Most cases with leukemic involvement are the small cell variant of ALCL. These cases often lack the pleomorphism seen in the common variant of ALCL and may be misdiagnosed. We report a series of three patients who presented with leukemic phase ALCL. The patients included an 11-year-old boy, a 29-year-old man, and a 59-year-old woman. The clinical and pathologic features of these cases are reviewed. The patients in our case series with leukemic phase ALCL exhibited rare clinical features. The patients presented with massive extranodal disease involving cerebrospinal fluid (CSF), liver, spleen, lungs, and bone marrow. CSF involvement was documented morphologically as well as by flow cytometry in two patients. Two of the patients had small cell variant and the third patient had common type ALCL. The neoplastic cells in all three patients were ALK positive; however these patients died within months of diagnosis. Leukemic phase ALCL is rare, and behaves in an aggressive manner. Some, but not all, cases in the literature presenting with peripheral blood involvement had small cell variant ALCL, as seen in two of our cases. The leukemic phase of ALCL should be considered when a T-cell leukemia with unusual morphologic features is encountered.

Anaplastic Large‐Cell Lymphoma, T‐/Null‐Cell Type

Anaplastic large-cell lymphoma, T-/null-cell type (ALCL), is a rare disease that has only been well characterized for two decades. Despite this, the biology of ALCL is better understood than that of many other more common variants of lymphoma. This review focuses on the pathophysiology, clinical presentation, and therapy of ALCL, including stem cell transplantation. In particular, the text emphasizes how novel prognostic features and the evolving understanding of the biology of this disease will influence treatment selection and drug development.

Expression pattern of intracellular leukocyte-associated proteins in primary mediastinal B cell lymphoma

Two microarray studies of mediastinal B cell lymphoma have shown that this disease has a distinct gene expression profile, and also that this is closest to the pattern seen in classical Hodgkin's disease. We reported previously an immunohistologic study in which the loss of intracellular B cell-associated signaling molecules in Reed-Sternberg cells was demonstrated, and in this study we have investigated the expression of the same components in more than 60 mediastinal B cell lymphomas. We report that these signaling molecules are frequently present, and in particular that Syk, BLNK and PLC-gamma2 (absent from Reed-Sternberg cells) are present in the majority of mediastinal B cell lymphomas. The overall pattern of B cell signaling molecules in this disease is therefore closer to that of diffuse large B cell lymphoma than to Hodgkin's disease, and is consistent with a common cell of origin as an explanation of the similar gene expression profiles.

Anaplastic lymphoma kinase proteins in growth control and cancer

The normal functions of full-length anaplastic lymphoma kinase (ALK) remain to be completely elucidated. Although considered to be important in neural development, recent studies in Drosophila also highlight a role for ALK in gut muscle differentiation. Indeed, the Drosophila model offers a future arena for the study of ALK, its ligands and signalling cascades. The discovery of activated fusion forms of the ALK tyrosine kinase in anaplastic large cell lymphoma (ALCL) has dramatically improved our understanding of the pathogenesis of these lymphomas and enhanced the pathological diagnosis of this subtype of non-Hodgkin's lymphoma (NHL). Likewise, the realisation that a high percentage of inflammatory myofibroblastic tumours express activated-ALK fusion proteins has clarified the causation of these mesenchymal neoplasms and provided for their easier discrimination from other mesenchymal-derived inflammatory myofibroblastic tumour (IMT) mimics. Recent reports of ALK expression in a range of carcinoma-derived cell lines together with its apparent role as a receptor for PTN and MK, both of which have been implicated in tumourigenesis, raise the possibility that ALK-mediated signalling could play a role in the development and/or progression of a number of common solid tumours. The therapeutic targeting of ALK may prove to have efficacy in the treatment of many of these neoplasms.

Three children with CD30 cutaneous anaplastic large cell lymphomas bearing the t(2;5)(p23;q35) translocation

Since its discovery in CD30(+) anaplastic large cell lymphomas, the t(2;5)(p23;q35) translocation has shown a high degree of association with nodal disease, younger patient age, and better prognosis. Furthermore, primary cutaneous CD30(+) anaplastic large cell lymphomas rarely manifests the t(2;5) translocation. We present three cases of this disease that occurred in children, bore the t(2;5) translocation, and had excellent outcomes, but presented cutaneously. Two of these lesions were primary skin lymphomas. Review of the available literature in conjunction with these three cases suggests that the t(2;5) translocation may be more strongly associated with younger patient age and favorable outcomes rather than nodal versus cutaneous site of presentation.

ALK-positive anaplastic large-cell lymphoma: strong T and B anti-tumour responses may cause hypocellular aspects of lymph nodes mimicking inflammatory lesions

The anaplastic large cell lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) is a rare type of non-Hodgkin lymphoma which occurs in children mostly. The ALK protein is highly immunogenic and elicits both humoral and cellular immune responses. A 15-yr-old child presented with fever and adenopathy and did not respond to antibiotics. Biopsy of the enlarged lymph node contained almost no lymphoid element except for a few CD8-positive T cells, plasma cells and isolated CD30-positive blasts. The patient's condition improved following lymphadenectomy but relapse occurred 3 months later with multiple nodes, high fever and an abdominal mass. This time an ALK-positive ALCL was diagnosed and the retrospective analysis of the initial biopsy revealed rare, isolated ALK+ cells. Molecular analysis showed T-cell clones and oligoclonal B cells in both biopsies and peripheral blood of the patient. The tumour cells harbour a t(2;5) translocation, revealing a null phenotype by immunohistochemistry and no evidence for T-cell clonality by Southern blotting. The patient's serum contained anti-ALK antibodies. Our findings suggest that the T-cell clones and anti-ALK antibodies in this patient constitute an anti-tumour response that caused the hypocellularity of the initial lymph node. Hypocellular and oedematous lymph nodes occurring in a child with evocative symptoms should be tested for the presence of ALK.

Expression of B-lymphocyte-associated transcription factors in human T-cell neoplasms

In this study we have investigated the expression of three B-cell-associated transcription factors in normal lymphoid tissue and in T-cell neoplasms (three cell lines, and more than 50 biopsy samples). Nuclear OCT-1 immunoreactivity was seen in normal B cells, in many extrafollicular T cells, and in a heterogeneous pattern (ranging in intensity from weak to moderate) in most T-cell neoplasms. OCT-2 immunostaining was primarily restricted in normal lymphoid tissue to B cells, and was absent from most T-cell neoplasms. In contrast, immunostaining for BOB-1/OCA-B--essentially restricted to B cells in normal lymphoid tissue, with the exception of activated T-lymphocytes--was seen in all of the T-cell lines tested and the majority of the tumor cells in all categories of T-cell lymphoma. Thus labeling for each of these three B-cell-associated transcription factors can be seen to varying degrees in T-cell neoplasms. However, the high frequency of BOB-1 expression in T-cell neoplasms, in contrast to its absence from resting peripheral T cells, suggests that its expression might be a prerequisite for neoplastic transformation, and prompts a search for the transcriptional target(s) of this factor in T cells.

Expression and functional analysis of the anaplastic lymphoma kinase (ALK) gene in tumor cell lines

The initial identification of the ALK gene, expressed as C-terminal part of the transforming fusion protein NPM-ALK in the t(2;5)(p23;q35) lymphoma-associated chromosomal translocation, revealed a novel receptor tyrosine kinase (RTK). In order to expand the knowledge on ALK expression in the human system, we examined a panel of human cell lines for ALK expression and found that transcription is completely repressed in cell lines of entodermal origin (0/21). Furthermore, full length receptor expression is absent in cell lines of the hematopoietic system with the exception of t(2;5)-associated anaplastic large cell lymphomas lines (ALCL), which are known to express chimeric NPM-ALK mRNA. Cell lines established from solid tumors of ectodermal origin, including melanoma and breast carcinoma, exhibited widespread mRNA expression of the ALK receptor at a broad range (53/64), an association which was found to be strongest in cell lines derived from neuroblastoma (6/6), glioblastoma (8/8) as well as in cell lines established from Ewing sarcoma (4/4) and retinoblastomas (2/2). Because of the reported involvement of neutrophin tyrosine kinase receptors in autocrine differentiation in neuroblastomas, we analyzed cell lines positive for full length or chimeric ALK protein for the presence of phoshotyrosine residues within the intracellular region of ALK. While the constitutive activation of chimeric NPM-ALK molecules could be shown, no evidence was found for induced or constitutively activated ALK receptors in neuroblastoma, melanoma or breast carcinoma cell lines. Although the receptor could be shown to be consistently expressed with exclusive specificity in tissues developed from the ectoderm, our results do not support any involvement of ALK in the stimulation of tumorigenic cell growth or differentiation so far, indicating that ALK expression is a physiologic rather than a pathologic phenomenon.

Tyrosine kinase oncogenes in normal hematopoiesis and hematological disease

Tyrosine kinase oncogenes are formed as a result of mutations that induce constitutive kinase activity. Many of these tyrosine kinase oncogenes that are derived from genes, such as c-Abl, c-Fes, Flt3, c-Fms, c-Kit and PDGFRbeta, that are normally involved in the regulation of hematopoiesis or hematopoietic cell function. Despite differences in structure, normal function, and subcellular location, many of the tyrosine kinase oncogenes signal through the same pathways, and typically enhance proliferation and prolong viability. They represent excellent potential drug targets, and it is likely that additional mutations will be identified in other kinases, their immediate downstream targets, or in proteins regulating their function.

Diversity of genomic breakpoints in TFG-ALK translocations in anaplastic large cell lymphomas: identification of a new TFG-ALK(XL) chimeric gene with transforming activity

Anaplastic large cell lymphomas are associated with chromosomal aberrations involving the anaplastic lymphoma kinase (ALK) gene at 2p23 that result in the expression of novel chimeric ALK proteins with transforming properties. In most of these tumors, the t(2;5)(p23;q35) generates the NPM-ALK fusion gene. However, several studies have now demonstrated that genes other than NPM may be fused to the ALK gene. We have recently described two different ALK rearrangements involving the TRK-fused gene (TFG) in which the same portion of ALK was fused to different length fragments of the 5' TFG region. These two rearrangements encoded chimeric proteins of 85 kd (TFG-ALK(S)) and 97 kd (TFG-ALK(L)), respectively. In this study, we have identified a new ALK rearrangement in which the catalytic domain of ALK was fused to a larger fragment of the TFG gene (TFG-ALK(XL)), encoding for a fusion protein of 113 kd. Genomic analysis of these three TFG-ALK rearrangements revealed that the TFG breakpoints occur at introns 3, 4, and 5, respectively, whereas the ALK breakpoints always occur in the same intron. No homologous regions or known recombination sequences were found in these regions. Transfection experiments using NIH-3T3 fibroblasts showed a similar transforming efficiency of TFG-ALK variants compared with NPM-ALK. In addition, in common with NPM-ALK, the TFG-ALK proteins formed stable complexes with the signaling proteins Grb2, Shc, and PLC-gamma. In conclusion, these findings indicate that the TFG may use a variety of intronic breakpoints in ALK rearrangements generating fusion proteins of different molecular weights, but with similar transforming potential than NPM-ALK.

Proteins encoded by genes involved in chromosomal alterations in lymphoma and leukemia: clinical value of their detection by immunocytochemistry

Acquired chromosomal anomalies (most commonly translocations) in lymphoma and leukemia usually result in either activation of a quiescent gene (by means of immunoglobulin or T-cell-receptor promotors) and expression of an intact protein product, or creation of a fusion gene encoding a chimeric protein. This review summarizes current immunocytochemical studies of these 2 categories of oncogenic protein, with emphasis on the clinical relevance of their detection in diagnostic samples. Among the quiescent genes activated by rearrangement, expression of cyclin D1 (due to rearrangement of the CCND1 [BCL-1] gene) is a near-specific marker of t(11;14) in mantle cell lymphoma; BCL-2 expression distinguishes follicular lymphoma cells from their nonneoplastic counterparts in reactive germinal centers and appears to be an independent prognostic marker in diffuse large cell lymphoma; and TAL-1 (SCL) expression identifies T-cell acute lymphoblastic neoplasms in which this gene is activated. The protein products of other genes activated by chromosomal rearrangement have a role as markers of either lineage (eg, PAX-5 [B-cell-specific activator protein] for B cells, including B-lymphoblastic neoplasms), or maturation stage (eg, BCL-6 for germinal-center and activated B cells and MUM-1/IRF4 for plasma cells). Currently, no hybrid protein encoded by fusion genes is reliably detectable by antibodies recognizing unique junctional epitopes (ie, epitopes absent from the wild-type constituent proteins). Nevertheless, staining for promyelocytic leukemia (PML) protein will detect acute PML with t(15;17) because the microspeckled nuclear labeling pattern for PML-RARalpha is highly distinctive. Similarly, antibodies to the anaplastic lymphoma kinase (ALK) tyrosine kinase are valuable (because wild-type ALK is not found in normal lymphoid tissue) in detecting neoplasms (CD30-positive large T-cell lymphomas) with t(2;5) or its variants. Thus, immunocytochemical detection of the products of many rearranged genes in lymphoma and leukemia can be clinically informative and provide information on cellular and subcellular protein expression that cannot be inferred from studies based on messenger RNA.

Immunochemical studies of antigenic lymphoma-associated proteins

We have previously reported that plasma from patients with anaplastic lymphoma kinase (ALK)-positive lymphoma contains antibodies against the oncogenic kinase NPM-ALK protein characteristic of this disease. We investigated whether this reactivity represents a phenomenon unique to ALK-positive lymphoma by screening plasma from patients with follicular lymphoma for antibodies to BCL-2 protein. Eight out of 10 samples showed such reactivity (and in six cases gave specific staining of BCL-2-transfected cells). As these findings suggest a new biochemical approach to the identification of oncogenic proteins in lymphoma, we investigated whether antibodies present in patients with ALK-positive lymphoma can precipitate NPM-ALK in quantities which should be sufficient for further analysis. We found that plasma samples from all10 patients studied immunoprecipitated NPM-ALK asaprotein visible in silver-stained sodium dodecyl sulphatepolyacrylamide gels. Finally we demonstrated that NPM-ALK could be visualized more clearly if it were immunoprecipitated from extracts of cells in which newly synthesized proteins had been labelled with 35S and then identified by autoradiography. These results suggest a strategy for using patients' autoantibodies to screen for antibodies to other tumour-associated proteins.

Translocations involving anaplastic lymphoma kinase (ALK)

Anaplastic large-cell lymphoma (ALCL) comprises a group of non-Hodgkin's lymphomas (NHLs) that were first described in 1985 by Stein and co-workers and are characterized by the expression of the CD30/Ki-1 antigen (Stein et al., 1985). Approximately half of these lymphomas are associated with a typical chromosomal translocation, t(2;5)(p23;q35). Much confusion about the exact classification and clinicopathological features of this subgroup of NHL was clarified with the identification of NPM-ALK (nucleophosmin-anaplastic lymphoma kinase) as the oncogene created by the t(2;5) (Morris et al., 1994). With the discovery of NPM-ALK as the specific lymphoma gene mutation, this NHL subtype could be redefined on the molecular level. This achievement was enhanced by the availability of specific antibodies that recognize ALK fusion proteins in paraffin-embedded lymphoma tissues. Several excellent recent reviews have summarized the histopathological and molecular findings of ALCL and their use in the classification of this lymphoma entity (Anagnostopoulos and Stein, 2000; Benharroch et al., 1998; Drexler et al., 2000; Foss et al., 2000; Gogusev and Nezelof, 1998; Kadin and Morris, 1998; Ladanyi, 1997; Morris et al., 2001; Shiota and Mori, 1996; Skinnider et al., 1999; Stein et al., 2000). This review will focus on the molecular function and signal transduction pathways activated by ALK fusion oncogenes, with recent advances and possible clinical implications to be discussed.

Inhibition of tyrosine kinase activity induces caspase-dependent apoptosis in anaplastic large cell lymphoma with NPM-ALK (p80) fusion protein

OBJECTIVE

The t(2;5)(p23;q35) translocation creates a fusion gene NPM-ALK (p80) that encodes a product with tyrosine kinase activity believed to play an important role in development of anaplastic large cell lymphoma (ALCL). Our study was aimed to analyze tyrosine kinase activity and phosphotyrosine in ALCLs. We were also interested in determining the effect of tyrosine kinase inhibitors on survival of ALCL.

METHODS

Eleven cases of ALCL and three ALCL cell lines with t(2;5)(Karpas-299, SUPM2, SU-DHL-1) and 10 Hodgkin's disease (HD) samples were stained with anti-phosphotyrosine antibody. The tyrosine kinase activity, p80 phosphorylation, and the apoptotic effects of two tyrosine kinase inhibitors, herbimycin A and STI-571, were determined on ALCL cell lines.

RESULTS

Herbimycin A had showed both a time- and dose-dependent apoptotic effect on all three cell lines, while STI-571 demonstrated a minimal effect. Following herbimycin A treatment, a decrease in tyrosine kinase activity in the ALCL cell lines and inhibition in NPM-ALK (p80) autophosphorylation was demonstrated by immunoprecipitation and Western blotting. Herbimycin A-induced apoptosis was accompanied by caspase-3 activation. Furthermore, apoptosis induced by herbimycin A was blocked by both z-VAD-FMK and z-DEVD-FMK, suggesting a critical role of caspases.

CONCLUSIONS

These findings indicate that tyrosine kinase activity is a common characteristic of ALCLs and necessary for ALCL cell survival. These findings further suggest that therapies targeting tyrosine kinases, including p80, may have clinical utility.

CD30+ lymphoproliferative disorder: primary cutaneous anaplastic large cell lymphoma followed by lymphomatoid papulosis

CD30+ large anaplastic lymphoid cells are seen in anaplastic large cell lymphoma (ALCL), and also in lymphomatoid papulosis (LyP) and other lymphoproliferative disorders. It can be difficult precisely to categorize these disorders with CD30+ cells. We report a case of primary cutaneous CD30+ ALCL with systemic metastases in whom the clinical disease subsequently evolved into LyP. The patient was initially administered cisplatin and etoposide and made a good response. Eighteen months later, recurrent, self-healing cutaneous small nodules appeared around the original tumour site without any systemic involvement. Histopathological examination of the recurrent lesions revealed infiltration with a mixture of cells that included neutrophils, eosinophils and CD30+ large anaplastic cells cytologically identical with those in the primary lesion. The anaplastic cells in both the primary and recurrent lesions were positive for monoclonal antibodies CD30, CD25 and a monoclonal antibody directed against the chimeric protein p80(NPM-ALK). These observations suggest the possibility that the ALCL and the subsequent LyP represent different clinical manifestations of proliferation of the same clone.

Anaplastic lymphoma kinase proteins and malignancy

The anaplastic lymphoma kinase (ALK) gene fuses to the nucleophosmin (NPM) gene as a result of a (2;5) translocation associated with a subtype of human lymphoma (initially designated anaplastic large cell lymphoma [ALCL] or Ki-1/CD30-positive lymphoma). The immunocytochemical detection of NPM-ALK (and proteins encoded by other ALK fusion genes) has allowed the definition of a tumor entity, "ALK-positive lymphoma" (which shows only partial overlap with pathologists' diagnosis of ALCL), to be defined and is invaluable in distinguishing this disease from ALK-negative large cell lymphomas. Eight variant ALK fusion proteins have been identified. Some are expressed only in ALCL, some are found only in the nonhematopoietic neoplasm inflammatory myofibroblastic tumor (IMT), and some are present in both types of malignancy. The ALK gene is silent in adult tissues except for restricted sites within the nervous system (consequently, patients with ALK-positive lymphoma produce antibodies to the ALK protein) but is expressed in some neuroblastomas and rhabdomyosarcomas. Biochemical studies suggest an anti-apoptotic function of NPM-ALK, and this may contribute to oncogenesis. Although ALK-positive lymphomas have a generally good prognosis, new therapeutic regimens are still needed for patients whose disease is refractory to conventional treatment.

The NPM-ALK and the ATIC-ALK fusion genes can be detected in non-neoplastic cells

Anaplastic large cell lymphoma (ALCL) is frequently associated with the t(2;5)(p23;q35) translocation. It creates a NPM-ALK fusion gene, fusing the anaplastic lymphoma kinase (ALK) gene (2p23) and the nucleophosmin (NPM) gene (5q35). Other rearrangements involving the ALK gene have recently been shown to be associated with ALCL, among which the ATIC-ALK rearrangement resulting from the inv(2)(p23q35) translocation is probably the most recurrent. The aims of the present study were to investigate the presence of NPM-ALK and ATIC-ALK fusion genes in ALCL, using a real-time 5' exonuclease-based reverse-transcription polymerase chain reaction (RT-PCR). This sensitive technique was also applied to investigate whether both fusion genes might be detected in Hodgkin's disease cases and in reactive lymphoid tissue. Results of the RT-PCR were compared to ALK immunostaining, cytogenetics, and fluorescence in situ hybridization (FISH) results. RT-PCR detected the NPM-ALK and ATIC-ALK fusions at high levels in 8 and 3 of a total of 13 ALK-positive ALCL cases. One ALK-positive ALCL case was negative for both fusion genes analyzed but revealed a new ALK-related translocation t(2;17)(p23;q25) by cytogenetic and FISH analysis. In addition, of the eight ALK-positive ALCL cases that were strongly positive for the NPM-ALK fusion, three cases also showed the presence of the ATIC-ALK fusion, although at much lower levels. Similarly, out of the three strongly positive ATIC-ALK cases, one case was positive for the NPM-ALK fusion, at low levels. Finally, the NPM-ALK and the ATIC-ALK fusions were detected, at equally low levels, respectively in 13 and 5 ALK-negative ALCL cases, in 11 and 5 Hodgkin's disease cases and in 20 and 1 non-neoplastic lymphoid tissues. The distinction between the high- and low-level detection was confirmed by relative quantitative RT-PCR for a representative number of cases. Of interest is the fact that the high-level detection coincided with the presence of ALK gene rearrangement detected by cytogenetics and FISH and may reflect a central role of the transcript in the oncogenic mechanism of ALK-positive ALCL. Low-level detection is not supported by cytogenetics and FISH, presumably due to the presence of the transcripts in only a small minority of normal cells not detectable by these techniques. Our findings demonstrate that NPM-ALK and ATIC-ALK fusion transcripts may be detected in conditions other than ALK-positive ALCL including reactive lymphoid tissues, although at low levels, suggesting the presence of the transcripts in normal (bystander) cells. Moreover, they suggest that the ALK gene rearrangement by itself might be insufficient to induce tumor formation. They further question the validity of quantitative real-time RT-PCR for monitoring minimal residual disease in ALCL. Finally, the newly identified translocation t(2;17)(p23;q25) can be added to the list of ALK gene rearrangements occurring in ALK-positive ALCL.

Involvement of 2p23 in pulmonary inflammatory pseudotumors

Pulmonary inflammatory pseudotumors (IP) are rare mesenchymal proliferations that have a polymorphic histology and an unpredictable biologic behavior. The histologic spectrum of IP has led to uncertainty as to whether this tumor has a reactive or neoplastic pathogenesis. Reports of extrapulmonary IP have identified clonal chromosomal aberrations involving 2p23 in the region of the ALK gene. Using fluorescence in situ hybridization with a probe flanking the ALK gene at 2p23 and immunostaining for the ALK gene product, we studied formalin-fixed, paraffin-embedded tissues of pulmonary IP and found a subset (33%) with 2p23 aberrations. We suggest that chromosomal rearrangements and ALK immunostaining may be helpful in the diagnosis of a group of pulmonary IP and should be investigated as a potential tool for predicting their future biologic behavior. An association with anaplastic large-cell lymphoma was also observed. HUM PATHOL 32:428-433.

Molecular characterization of a new ALK translocation involving moesin (MSN-ALK) in anaplastic large cell lymphoma

The majority of anaplastic large cell lymphomas (ALCL) are associated with chromosomal abnormalities affecting the anaplastic lymphoma kinase (ALK) gene which result in the expression of hybrid ALK fusion proteins in the tumor cells. In most of these tumors, the hybrid gene comprises the 5' region of nucleophosmin (NPM) fused in frame to the 3' portion of ALK, resulting in the expression of the chimeric oncogenic tyrosine kinase NPM-ALK. However, other variant rearrangements have been described in which ALK fuses to a partner other than NPM. Here we have identified the moesin (MSN) gene at Xq11-12 as a new partner of ALK in a case of ALCL which exhibited a distinctive membrane-restricted pattern of ALK labeling. The hybrid MSN-ALK protein had a molecular weight of 125 kd and contained an active tyrosine kinase domain. The unique membrane staining pattern of ALK is presumed to reflect association of moesin with cell membrane proteins. In contrast to other translocations involving the ALK gene, the ALK breakpoint in this case occurred within the exonic sequence coding for the juxtamembrane portion of ALK. Identification of the genomic breakpoint confirmed the in-frame fusion of the whole MSN intron 10 to a 17 bp shorter juxtamembrane exon of ALK. The breakpoint in der(2) chromosome showed a deletion, including 30 bp of ALK and 36 bp of MSN genes. These findings indicate that MSN may act as an alternative fusion partner for activation of ALK in ALCL and provide further evidence that oncogenic activation of ALK may occur at different intracellular locations.

Will the “new biology” Affect the Future of Histopathology?

The technologies used in histopathology are changing as a consequence of the current revolutionary progress in several areas of biology. It is likely that general cancer management will improve because of the impact of molecular techniques and immunohistochemistry on tumor diagnosis and classification and on the determination of prognosis and response to therapy. Moreover, as therapies are starting to be modelled after the distinctive molecular characteristics of a specific tumor, the availability of molecular tests to all patients will become a matter of great importance.

CD30+ anaplastic large cell lymphoma: a review of its histopathologic, genetic, and clinical features

Anaplastic large cell lymphoma (ALCL) represents a generally recognized group of large cell lymphomas. Defining features consist of a proliferation of predominantly large lymphoid cells with strong expression of the cytokine receptor CD30 and a characteristic growth pattern. With the use of molecular and clinical criteria, 3 entities of ALCL have been identified: primary systemic anaplastic lymphoma kinase (ALK)+ ALCL, primary systemic ALK− ALCL, and primary cutaneous ALCL. ALK expression is caused by chromosomal translocations, most commonly t(2;5). ALK+ ALCL predominantly affects young male patients and, if treated with chemotherapy, has a favorable prognosis. It shows a broad morphologic spectrum, with the “common type,” the small cell variant, and the lymphohistiocytic variant being most commonly observed. The knowledge of the existence of these variants is essential in establishing a correct diagnosis. ALK− ALCL occurs in older patients, affecting both genders equally and having an unfavorable prognosis. The morphology and the immunophenotype of primary cutaneous ALCL show an overlap with that of lymphomatoid papulosis. Both diseases have an excellent prognosis, and secondary systemic dissemination is only rarely observed. The described ALCL entities usually derive from cytotoxic T cells. In contrast, large B-cell lymphomas with anaplastic morphology are believed to represent not a separate entity but a morphologic variant of diffuse large B-cell lymphoma. Malignant lymphomas with morphologic features of both Hodgkin disease and ALCL have formerly been classified as Hodgkin-like ALCL . Recent immunohistologic studies, however, suggest that ALCLs Hodgkin-like represent either cases of tumor cell–rich classic Hodgkin disease or (less commonly) ALK+ ALCL or ALK− ALCL.

Leukaemic small cell variant anaplastic large cell lymphoma during pregnancy

The history of a 28-year-old woman with anaplastic large cell lymphoma (ALCL) in the first trimester of her pregnancy is reported. Investigations allowed to diagnose a T-cell CD30 positive ALCL, which appearance is rare during pregnancy. Moreover, the atypical lymphoid cells were found in the peripheral blood and were predominantly small to medium sized with nuclear irregularities and cytoplasmic azurophilic granules, which allowed the hypothesis of leukaemic presentation of a small cell variant ALCL. A variant of the t(2:5)(p23:q35) was found [del(2)(p22)]. The patient died shortly after diagnosis.

Pathobiology of NPM-ALK and variant fusion genes in anaplastic large cell lymphoma and other lymphomas

Despite its clinical and histological heterogeneity, anaplastic large cell lymphoma (ALCL) is now a well-recognized clinicopathological entity accounting for 2% of all adult non-Hodgkin's lymphomas (NHL) and about 13% of pediatric NHL. Immunophenotypically, ALCL are of T cell (predominantly) or Null cell type; by definition, cases expressing B cell antigens are officially not included in this entity. The translocation (2;5)(p23;q35) is a recurring abnormality in ALCL; 46% of the ALCL patients bear this signature translocation. This translocation creates a fusion gene composed of nucleophosmin (NPM) and a novel receptor tyrosine kinase gene, named anaplastic lymphoma kinase (ALK). The NPM-ALK chimeric gene encodes a constitutively activated tyrosine kinase that has been shown to be a potent oncogene. The exact pathogenetic mechanisms leading to lymphomagenesis remain elusive; however, the synopsis of evidence obtained to date provides an outline of likely scenarios. Several t(2;5) variants have been described; in some instances, the breakpoints have been cloned and the genes forming a new fusion gene with ALK have been identified: ATIC-ALK, TFG-ALK and TPM3-ALK. Cloning the translocation breakpoint and identifying the ALK and NPM genes provided tools for screening material from patients with ALCL using various approaches at the chromosome, DNA, RNA, or protein level: positive signals in the reverse transcriptase-polymerase chain reaction (RT-PCR) and the immunostaining with anti-ALK monoclonal antibodies (McAb) serve as the most convenient tests for detection of the t(2;5) NPM-ALK since the fusion gene and ALK protein expression do not occur in normal or reactive lymphoid tissue. The wide range of NPM-ALK positivity reported in different series appears to be dependent on the inclusion and selection criteria of the ALCL cases studied. Overall, however, 43% of ALCL cases were NPM-ALK+ (83% of pediatric ALCL vs 31% of adult ALCL). Occasional non-ALCL B cell lymphomas (4%) with diffuse large cell and immunoblastic histology and Hodgkin's disease cases (3%) were NPM-ALK-, but these data are questionable. The aggregate results indicate that, in contrast to primary nodal (systemic) ALCL, the t(2;5) may be present in only 10-20% of primary cutaneous ALCL and rarely, if at all, in lymphomatoid papulosis, a potential precursor lesion; however, these 10-20% positive cases were not confirmed by anti-ALK McAb immunostaining and may represent an overestimate. Positivity for NPM-ALK is associated to various degrees with the following parameters: 44% and 45% of ALCL cases with T cell and Null cell immunophenotype, respectively, are positive, whereas only 8% of cases with a B cell immunoprofile are positive; the mean age of positive patients is significantly younger than that of negative patients; positive cases carry a better overall prognosis (but not in all studies). Recently, the homogenous category of ALK lymphoma ('ALKoma') has emerged as a distinct pathological entity within the heterogenous group of ALCL. The fact that patients with ALK lymphomas experience significantly better overall survival than ALK- ALCL demonstrates further that analysis of ALK expression has important prognostic implications. The term ALK lymphoma signifies a switch in the use of the diagnostic criteria: cases are selected on the basis of a genetic abnormality (the ALK rearrangement), instead of the review of morphological or immunophenotypical features which are clearly more prone to disagreement and controversy. Since its initial description in 1985 ALCL has become one of the best characterized lymphoma entities.

Immune response to the ALK oncogenic tyrosine kinase in patients with anaplastic large-cell lymphoma

Oncogenic anaplastic lymphoma kinase (ALK) fusion proteins (nucleophosmin–ALK [NPM-ALK] and other variants) are expressed in many cases of anaplastic large-cell lymphoma (ALCL) but are absent from normal tissues. The possibility that ALK proteins are immunogenic was investigated with the use of an immunocytochemical technique to screen plasma from ALK-positive ALCL on transfectants expressing ALK proteins and by an in vitro kinase assay. Circulating antibodies against NPM-ALK protein were present in all ALK-positive ALCL patients (11 out of 11 cases) studied while 10 patients also had antibodies recognizing normal ALK protein. Weak antibodies reactive with NPM-ALK (which may represent anti-NPM autoantibodies) were detected by the in vitro kinase assay in 3 of the 10 control samples (but not by immunocytochemistry). The presence of anti-ALK antibodies may be relevant to the relatively good prognosis of ALK-positive ALCL. The immunocytochemical technique for detecting anti-ALK activity is simple and semiquantative and may provide a means of detecting B-cell responses to other tumor-associated molecules.

Immune response to the ALK oncogenic tyrosine kinase in patients with anaplastic large-cell lymphoma

Oncogenic anaplastic lymphoma kinase (ALK) fusion proteins (nucleophosmin–ALK [NPM-ALK] and other variants) are expressed in many cases of anaplastic large-cell lymphoma (ALCL) but are absent from normal tissues. The possibility that ALK proteins are immunogenic was investigated with the use of an immunocytochemical technique to screen plasma from ALK-positive ALCL on transfectants expressing ALK proteins and by an in vitro kinase assay. Circulating antibodies against NPM-ALK protein were present in all ALK-positive ALCL patients (11 out of 11 cases) studied while 10 patients also had antibodies recognizing normal ALK protein. Weak antibodies reactive with NPM-ALK (which may represent anti-NPM autoantibodies) were detected by the in vitro kinase assay in 3 of the 10 control samples (but not by immunocytochemistry). The presence of anti-ALK antibodies may be relevant to the relatively good prognosis of ALK-positive ALCL. The immunocytochemical technique for detecting anti-ALK activity is simple and semiquantative and may provide a means of detecting B-cell responses to other tumor-associated molecules.

TPM3-ALK and TPM4-ALK oncogenes in inflammatory myofibroblastic tumors

Inflammatory myofibroblastic tumors (IMTs) are neoplastic mesenchymal proliferations featuring an inflammatory infiltrate composed primarily of lymphocytes and plasma cells. The myofibroblastic cells in some IMTs contain chromosomal rearrangements involving the ALK receptor tyrosine-kinase locus region (chromosome band 2p23). ALK-which is normally restricted in its expression to neural tissues-is expressed strikingly in the IMT cells with 2p23 rearrangements. We now report a recurrent oncogenic mechanism, in IMTs, in which tropomyosin (TPM) N-terminal coiled-coil domains are fused to the ALK C-terminal kinase domain. We have cloned two ALK fusion genes, TPM4-ALK and TPM3-ALK, which encode approximately 95-kd fusion oncoproteins characterized by constitutive kinase activity and tyrosylphosphorylation. Immunohistochemical and molecular correlations, in other IMTs, implicate non-TPM ALK oncoproteins that are predominantly cytoplasmic or pre- dominantly nuclear, presumably depending on the subcellular localization of the ALK fusion partner. Notably, a TPM3-ALK oncogene was reported recently in anaplastic lymphoma, and TPM3-ALK is thereby the first known fusion oncogene that transforms, in vivo, both mesenchymal and lymphoid human cell lineages.

Anaplastic large-cell lymphomas of B-cell phenotype are anaplastic lymphoma kinase (ALK) negative and belong to the spectrum of diffuse large B-cell lymphomas

There is controversy in the literature as to whether anaplastic large-cell lymphoma of B-cell phenotype is related to the t(2;5)-positive T- or 'null' cell lymphoma of the same morphology. We report a study of 24 lymphomas with morphological features of anaplastic large-cell lymphoma which expressed one or more B-cell markers and lacked T-lineage markers. Clinical features were more in keeping with large B-cell lymphoma than with classical t(2;5)-positive anaplastic large-cell lymphoma, and immunostaining for anaplastic lymphoma kinase (ALK) protein provided no evidence for the (2;5) translocation (or one of its variants). The staining patterns for CD20 and CD79 were typical of diffuse large B-cell lymphoma, CD30 expression was variable, and most cases (15/22) lacked epithelial membrane antigen (EMA). These findings support the view that 'B-cell anaplastic large-cell lymphoma' is unrelated to t(2;5)-positive (ALK-positive) lymphoma, and that it represents a morphological pattern occasionally encountered among diffuse large B-cell lymphomas. By the same reasoning, most tumours diagnosed as 'ALK-negative anaplastic large-cell lymphoma of T-cell or null phenotype' probably belong to the spectrum of peripheral T-cell lymphomas.

Further demonstration of the diversity of chromosomal changes involving 2p23 in ALK-positive lymphoma: 2 cases expressing ALK kinase fused to CLTCL (clathrin chain polypeptide-like)

Anaplastic lymphoma kinase (ALK)-positive lymphomas are characterized by expression of a hybrid protein, comprising the cytoplasmic portion of the ALK tyrosine kinase fused to a partner protein. This hybrid kinase is often encoded by the nucleophosmin (NPM)NPM-ALK fusion gene resulting from the (2;5)(p23;q35) chromosomal translocation. However, the ALK gene at 2p23 may also be involved in 2 variant translocations, namely t(1;2)(q25;p23) and t(2;3)(p23;q21), which create the TPM3-ALK andTFG-ALK fusion genes, respectively. We report here 2 lymphomas with an unusual finely granular cytoplasmic ALK staining pattern, clearly different from the pattern observed in ALK-positive lymphomas carrying NPM-ALK or its variants. A cloned complementary DNA sequence from 1 of these 2 lymphomas contained the ALK gene fused to the second clathrin heavy chain gene (also referred to as clathrin heavy polypeptide-like gene) (CLTCL). The distinctive granular cytoplasmic staining pattern for ALK was likely to be due to binding of the fusion protein to clathrin-coated vesicles. TheCLTCL gene is constitutively expressed in lymphoid cells and therefore presumably contributes an active promoter for theCLTCL-ALK gene. The fusion protein had a molecular weight (250 kd) that differs from all known ALK products, and it was autophosphorylated in an in vitro kinase assay, confirming that it is constitutively active and hence capable of contributing to malignant transformation. These 2 cases, therefore, represent a hitherto undescribed mechanism of ALK activation in lymphoma and further illustrate the diversity of fusion partners for the ALKgene.

Further demonstration of the diversity of chromosomal changes involving 2p23 in ALK-positive lymphoma: 2 cases expressing ALK kinase fused to CLTCL (clathrin chain polypeptide-like)

Anaplastic lymphoma kinase (ALK)-positive lymphomas are characterized by expression of a hybrid protein, comprising the cytoplasmic portion of the ALK tyrosine kinase fused to a partner protein. This hybrid kinase is often encoded by the nucleophosmin (NPM)NPM-ALK fusion gene resulting from the (2;5)(p23;q35) chromosomal translocation. However, the ALK gene at 2p23 may also be involved in 2 variant translocations, namely t(1;2)(q25;p23) and t(2;3)(p23;q21), which create the TPM3-ALK andTFG-ALK fusion genes, respectively. We report here 2 lymphomas with an unusual finely granular cytoplasmic ALK staining pattern, clearly different from the pattern observed in ALK-positive lymphomas carrying NPM-ALK or its variants. A cloned complementary DNA sequence from 1 of these 2 lymphomas contained the ALK gene fused to the second clathrin heavy chain gene (also referred to as clathrin heavy polypeptide-like gene) (CLTCL). The distinctive granular cytoplasmic staining pattern for ALK was likely to be due to binding of the fusion protein to clathrin-coated vesicles. TheCLTCL gene is constitutively expressed in lymphoid cells and therefore presumably contributes an active promoter for theCLTCL-ALK gene. The fusion protein had a molecular weight (250 kd) that differs from all known ALK products, and it was autophosphorylated in an in vitro kinase assay, confirming that it is constitutively active and hence capable of contributing to malignant transformation. These 2 cases, therefore, represent a hitherto undescribed mechanism of ALK activation in lymphoma and further illustrate the diversity of fusion partners for the ALKgene.

Expression of the ALK tyrosine kinase gene in neuroblastoma

ALK (anaplastic lymphoma kinase) is a tyrosine kinase receptor, expressed as part of the chimeric NPM-ALK protein, in anaplastic large cell lymphomas (ALCLs) exhibiting the t(2;5)(p23;q35) translocation. As a result of this translocation, the NPM (nucleophosmin) gene is fused to the portion of the ALK gene encoding its intracytoplasmic segment. In normal mouse tissues, mRNA encoding the Alk receptor has been found only in neural cells, suggesting involvement of this receptor in the development of the nervous system. The purpose of the present study was to examine the presence of ALK transcripts and protein in normal human tissues and a variety of cell lines and human tumors. Emphasis was placed on neuroblastomas because other tyrosine kinase receptors are expressed in human neuroblastomas. Fifty-six cell lines, including 29 lines of neural origin, and lymphoid and nonlymphoid tissue specimens, including 24 neuroblastomas, were investigated for ALK expression, using reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry. The results confirmed that mRNA encoding ALK protein was not detectable in any normal or neoplastic hematopoietic tissue tested, except for t(2;5)-positive ALCL. The salient finding was that 13 of the 29 cell lines of neural origin and 22 of 24 neuroblastomas were found to express ALK transcripts and ALK protein. However, no correlation was evident between any known prognostic factors and the level of ALK expression.

ATIC-ALK: A novel variant ALK gene fusion in anaplastic large cell lymphoma resulting from the recurrent cryptic chromosomal inversion, inv(2)(p23q35)

The subset of CD30-positive anaplastic large cell lymphomas (ALCL) with the NPM-ALK gene fusion arising from the t(2;5)(p23;q35) forms a distinct clinical and prognostic entity. Recently, various cytogenetic, molecular, and protein studies have provided evidence for the existence of several types of variant ALK fusions in up to 20% of ALK+ ALCL, of which only one, a TPM3-ALK fusion resulting from a t(1;2)(q25;p23), has so far been cloned. A cryptic inv(2)(p23q35) has been described as another recurrent cytogenetic alteration involving ALK and an unidentified fusion partner in some ALCL. In a screen for variant ALK gene fusions, we identified two ALCL that were negative for NPM-ALK by reverse transcriptase-polymerase chain reaction, but were positive for cytoplasmic ALK with both polyclonal and monoclonal antibodies to the ALK tyrosine kinase domain, consistent with ALK deregulation by an alteration other than the t(2;5) Case 1 was a T-lineage nodal and cutaneous ALCL in a 52-year-old woman, and Case 2 was a T-lineage nodal ALCL in a 12-year-old girl. FISH analysis confirmed ALK rearrangement in both cases. An inverse polymerase chain reaction approach was then used to identify the ALK translocation partner in Case 1. We found an in-frame fusion of ALK to ATIC, a gene previously mapped to 2q34-q35. We then confirmed by DNA polymerase chain reaction the localization of ATIC to yeast artificial chromosome (YAC) 914E7 previously reported to span the 2q35 break in the inv(2)(p23q35). FISH analysis in Case 1 confirmed rearrangement of YAC 914E7 and fusion to ALK. The ATIC-ALK fusion was confirmed in Case 1 and also identified in Case 2 by conventional reverse transcriptase-polymerase chain reaction using ATIC forward and ALK reverse primers. ATIC encodes an enzyme involved in purine biosynthesis which, like other fusion partners of ALK, is constitutively expressed and appears to contain a dimerization domain. ATIC-ALK fusion resulting from the inv(2)(p23q35) thus provides a third mechanism of ALK activation in ALK+ ALCL.

Anaplastic large cell lymphoma: a clinicopathologic analysis

The clinicopathologic features of anaplastic large cell lymphoma (ALCL) are reviewed. ALCL is a heterogeneous group of tumours, and histologic examination alone is not adequate in providing useful prognostic information. However, using a combination of clinical, phenotypic, and genotypic features, several distinct clinicopathologic entities have been identified. A subset of ALCL as presently defined is characterized by a balanced translocation, t(2;5)(p23;q35), resulting in a novel fusion protein (NPM-ALK) that can be readily detected by immunohistochemical methods using antibodies against the ALK protein. Detection of ALK protein, along with other methods for demonstrating the t(2;5), has assisted in identifying a distinct biologic entity within the heterogeneous group of ALCL with significant prognostic implications. It is important to separate these from cases of ALK-negative ALCL, which have a poorer prognosis, and cases of primary cutaneous ALCL, which have an excellent prognosis.