Aberrant ALK tyrosine kinase signaling. Different cellular lineages, common oncogenic mechanisms

Crizotinib in patients with advanced, inoperable inflammatory myofibroblastic tumours with and without anaplastic lymphoma kinase gene alterations (European Organisation for Research and Treatment of Cancer 90101 CREATE): a multicentre, single-drug, prospective, non-randomised phase 2 trial

BACKGROUND

An inflammatory myofibroblastic tumour (IMFT) is a rare mesenchymal neoplasm characterised by anaplastic lymphoma kinase (ALK) gene rearrangements. We assessed the activity and safety of crizotinib, a tyrosine kinase inhibitor, targeting ALK in patients with advanced IMFT either with or without ALK alterations.

METHODS

We did a multicentre, biomarker-driven, single-drug, non-randomised, open-label, two-stage phase 2 trial (European Organisation for Research and Treatment of Cancer 90101 CREATE) at 13 study sites (five university hospitals and eight specialty clinics) in eight European countries (Belgium, France, Germany, Italy, Netherlands, Poland, Slovakia, and the UK). Eligible participants were patients aged at least 15 years with a local diagnosis of advanced or metastatic IMFT deemed incurable with surgery, radiotherapy, or systemic therapy; measurable disease; an Eastern Cooperative Oncology Group performance status of 0-2; and adequate haematological, renal, and liver function. Central reference pathology was done for confirmation of the diagnosis, and ALK positivity or negativity was assessed centrally using immunohistochemistry and fluorescence in-situ hybridisation based on archival tumour tissue and defined as ALK immunopositivity or rearrangements in at least 15% of tumour cells. Eligible ALK-positive and ALK-negative patients received oral crizotinib 250 mg twice per day administered on a continuous daily dosing schedule (the duration of each treatment cycle was 21 days) until documented disease progression, unacceptable toxicity, or patient refusal. If at least two of the first 12 eligible and assessable ALK-positive patients achieved a confirmed complete or partial response according to Response Evaluation Criteria in Solid Tumors (RECIST) 1.1, a maximum of 35 patients were to be enrolled. If at least six ALK-positive patients achieved a confirmed response, the trial would be deemed successful. The primary endpoint was the proportion of patients who achieved an objective response (ie, a complete or partial response) as per RECIST 1.1, with response confirmation assessed by the local investigator every other cycle. Activity and safety endpoints were analysed in the per-protocol population. This trial is registered with ClinicalTrials.gov, number NCT01524926.

FINDINGS

Between Oct 3, 2012, and April 12, 2017, we recruited and treated 20 eligible participants, 19 of whom were assessable for the primary endpoint. Median follow-up was 863 days (IQR 358-1304). Six of 12 ALK-positive patients (50%, 95% CI 21·1-78·9) and one of seven ALK-negative patients (14%, 0·0-57·9) achieved an objective response. The most common treatment-related adverse events in the 20 participants were nausea (11 [55%]), fatigue (9 [45%]), blurred vision (nine [45%]), vomiting (seven [35%]), and diarrhoea (seven [35%]). Eight serious adverse events occurred in five patients: pneumonia, fever of unknown cause, a heart attack with increased creatinine and possible sepsis, an abdominal abscess with acute renal insufficiency, and a QT prolongation.

INTERPRETATION

With 50% of participants with ALK-positive tumours achieving an objective response, crizotinib met the prespecified criteria for success in this trial. The results presented here support the rationale for inhibiting ALK in patients with IMFT. Crizotinib could be considered as the standard of care for patients with locally advanced or metastatic ALK-positive IMFT who do not qualify for curative surgery.

FUNDING

The European Organisation for Research and Treatment of Cancer and Pfizer.

ALK as a paradigm of oncogenic promiscuity: different mechanisms of activation and different fusion partners drive tumors of different lineages

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase protein implicated in a variety of hematological malignancies and solid tumors. Since the identification of the ALK gene in 1994 as the target of the t(2;5) chromosomal translocation in anaplastic large cell lymphoma, ALK has been proven a remarkably promiscuous oncogene. ALK contributes to the development of a notable assortment of tumor types from different lineages, including hematolymphoid, mesenchymal, epithelial and neural tumors, through a variety of genetic mechanisms: gene fusions, activating point mutations, and gene amplification. Recent developments led to significant diagnostic and therapeutic advances, including efficient diagnostic tests and ALK-targeting agents readily available in the clinical setting. This review addresses some therapeutic considerations of ALK-targeted agents and the biologic implications of ALK oncogenic promiscuity, but the main points discussed are: 1) the variety of mechanisms that result in activation of the ALK oncogene, with emphasis on the promiscuous partnerships demonstrated in chromosomal rearrangements; 2) the diversity of tumor types of different lineages in which ALK has been implicated as a pathogenic driver; and 3) the different diagnostic tests available to identify ALK-driven tumors, and their respective indications.

Emerging therapeutic targets for soft tissue sarcoma

Soft tissue sarcomas (STS) are malignancies of mesenchymal origin that represent approximately 1% of cancers in adults. Systematic research into the treatment of STS is challenging given its rarity and disease heterogeneity. Despite the ability to histologically subtype STS, only recently has our approach to therapy begun to differentiate along these lines. The purpose of this review is to highlight emerging therapeutic targets and therapies that hold the potential to add to the current state of systemic treatment for STS.

The immunohistochemistry laboratory: looking at molecules and preparing for tomorrow

CONTEXT

Surgical and subspecialty pathologists rely heavily on the patient's clinical context, imaging studies, morphology, and on ancillary studies such as immunohistochemistry (IHC), cytogenetics, and molecular diagnostics in arriving at accurate, contemporary diagnoses. Lymphoma/leukemia classification has led the way in the number of antibodies used in IHC algorithmic diagnostic approaches to distinguish more than 40 diseases. As the era of genomics, transcriptomics, proteomics, and targeted pathway therapeutics unfolds-and as infusion of federal funds to programs such as Accelerating Clinical Trials of Novel Oncologic PathWays (ACTNOW) requires that correlative biomarker assays be performed in Clinical Laboratory Improvement Amendments of 1988 (CLIA)-certified IHC laboratories-we face changes and challenges for the future.

OBJECTIVE

To discuss the laboratory, pertinent daily diagnostic, prognostic, and therapeutic uses of IHC, and future directions and challenges.

DATA SOURCES

Recent literature review and ongoing current activities in our laboratory and institution.

CONCLUSIONS

Meticulous attention at the microscope by expert subspecialty pathologists using ancillary methods is important in making correct diagnoses. Awareness of the literature and interactions with our research colleagues, including clinical, basic, and translational scientists, continue to expand our insights into and understanding of complex diseases; this will ultimately provide prognostic information to assist in appropriate clinical management of our patients and development of new targeted or combination therapies. Multimodality correlations will continue, with morphology, imaging data, immunophenotyping, and genetics as well as steadily increasing integration of pathway signaling, genome, sequenome, transcriptome, and proteome data used in clinical settings.

Crizotinib in ALK-rearranged inflammatory myofibroblastic tumor

Inflammatory myofibroblastic tumor (IMT) is a distinctive mesenchymal neoplasm characterized by a spindle-cell proliferation with an inflammatory infiltrate. Approximately half of IMTs carry rearrangements of the anaplastic lymphoma kinase (ALK) locus on chromosome 2p23, causing aberrant ALK expression. We report a sustained partial response to the ALK inhibitor crizotinib (PF-02341066, Pfizer) in a patient with ALK-translocated IMT, as compared with no observed activity in another patient without the ALK translocation. These results support the dependence of ALK-rearranged tumors on ALK-mediated signaling and suggest a therapeutic strategy for genomically identified patients with the aggressive form of this soft-tissue tumor. (Funded by Pfizer and others; ClinicalTrials.gov number, NCT00585195.).

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.

Inflammatory myofibroblastic tumor: comparison of clinicopathologic, histologic, and immunohistochemical features including ALK expression in atypical and aggressive cases

Inflammatory myofibroblastic tumor (IMT) is a neoplasm of intermediate biologic potential. In this study, we report a subset of IMTs with histologic atypia and/or clinical aggressiveness that were analyzed for clinicopathologic features, outcome, and immunohistochemical expression of anaplastic lymphoma kinase (ALK) and other markers to identify potential pathologic prognostic features. Fifty-nine IMTs with classic morphology (5 cases), atypical histologic features (21 cases), local recurrence (27 cases), and/or metastasis (6 cases) were studied. Immunohistochemistry was performed for ALK1 and other markers (Mib-1, c-Myc, cyclin D1, caspase 3, Bcl-2, Mcl-1, survivin, p27, CD56, p53, MDM-2) using standard techniques. The 59 IMTs had an age at diagnosis ranging from 3 weeks to 74 years (mean 13.2 y, median 11 y, 44% in the first decade). The mean tumor size was 7.8 cm. Sites included the abdomen or pelvis in 64%, lung in 22%, head and neck in 8%, and extremities in 5%. The follow-up ranged from 3 months to 11 years, with a mean of 3.6 years and a median of 3 years. Thirty-three patients had local recurrences, including 13 with multiple local recurrences and 6 patients with both local recurrences and distant metastases. Six patients died of disease, 5 with local recurrences, and 1 with distant metastases. Histologic evolution to a more pleomorphic cellular, spindled, polygonal, or round cell morphologic pattern was observed in 7 cases. Abdominal and pelvic IMTs had a recurrence rate of 85%. Recurrent and metastatic IMTs were larger, with mean diameters of 8.7 and 11 cm, respectively. Cytoplasmic ALK reactivity was seen in 56%. ALK-negative IMTs occurred in older patients (mean age 20.1) years and had greater nuclear pleomorphism, atypia, and atypical mitoses. All 6 metastatic IMTs were ALK-negative. Nuclear expression of p53 was detected in 80% of IMTs overall, but in only 25% of the metastatic subset. There were no significant differences among the subgroups for c-Myc, cyclin D1, MDM-2, Mcl-1, Bcl-2, CD56, p27, caspase 3, or survivin expression. In conclusion, among these 59 IMTs, ALK reactivity was associated with local recurrence, but not distant metastasis, which was confined to ALK-negative lesions. Absent ALK expression was associated with a higher age overall, subtle histologic differences, and death from disease or distant metastases (in a younger subset). Other proliferative, apoptotic, and prognostic markers did not correlate well with morphology or outcome. Thus, ALK reactivity may be a favorable prognostic indicator in IMT and abdominopelvic IMTs recur more frequently.

Identification of squamous cell carcinoma associated proteins by proteomics and loss of beta tropomyosin expression in esophageal cancer

AIM: To assess the proteome of normal versus tumor tissue in squamous cell carcinoma of the esophagus (SCCE) in Iranian patients and compare our results with former reports by using proteomics.

METHODS: Protein was extracted from normal and tumor tissues. Two dimensional electrophoresis was carried out and spots with differential expression were identified with mass spectrometry. RNA extraction and RT-PCR along with immunodetection were performed.

RESULTS: Fourteen proteins were found whose expression levels differed in tumor compared to normal tissues. Mass spectrometric analysis resulted in the identification of β-tropomyosin (TMβ), myosin light chain 2 (and its isoform), myosin regulatory light chain 2, peroxyredoxin 2, annexinIand an unknown polypeptide as the down regulated polypeptides in tumor tissue. Heat shock protein 70 (HSP70), TPM4-ALK fusion oncoprotein 2, myosin light polypeptide 6, keratinI, GH16431p and calreticulin were the up-regulated polypeptides found in tumor tissue. Several of these proteins, such as TMβ, HSP70, annexinI, calreticulin, TPM4-ALK and isoforms of myosins, have been well recognized in tumorigenesis of esophageal or other types of cancers.

CONCLUSION: Our study not only supports the involve-ment of some of the formerly reported proteins in SCCE but also introduces additional proteins found to be lost in SCCE, including TMβ.

ETV6–NTRK3: a chimeric protein tyrosine kinase with transformation activity in multiple cell lineages

The ETV6-NTRK3 (TEL-TRKC) gene fusion was discovered by breakpoint analysis of the t(12;15)(p13;q25) translocation associated with congenital fibrosarcoma, a pediatric soft tissue malignancy. ETV6-NTRK3 (EN) encodes the sterile alpha motif oligomerization domain of the ETV6 (TEL) transcription factor linked to the protein tyrosine kinase domain of the neurotrophin-3 receptor NTRK3 (TRKC). The EN chimeric oncoprotein links to multiple signaling cascades including Ras-MAP kinase and PI3K-AKT through the IRS-1 adapter protein. Recent evidence indicates that a functional insulin-like growth factor 1 receptor axis and higher order polymer formation are essential for EN oncogenesis. EN has been detected in other malignancies, including secretory breast carcinoma. This chimeric oncoprotein is therefore unique in being expressed in tumors derived from multiple cell lineages.

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.

Inflammatory fibroid polyps of the gastrointestinal tract: evidence for a dendritic cell origin

Inflammatory fibroid polyps (IFPs) are rare mesenchymal tumors of the gastrointestinal tract that consist of spindle-shaped stromal cells and an inflammatory infiltrate rich in eosinophils. Their etiology and histogenesis remain unknown. Based on previous reports of their immunoreactivity for CD34 and c-kit biomarkers, IFPs have been thought to be related to gastrointestinal stromal tumors (GISTs). After reviewing the current literature and examining IFPs at the light microscopic level, we evaluated a series of IFPs using an extensive panel of immunohistochemical and in situ hybridization markers in an effort to gain insight into their etiology and histogenesis and to determine their true relationship to GISTs. Sixteen routinely processed IFP specimens (14 gastric, 1 ileal, and 1 rectal) were immunohistochemically stained for antibodies to CD34, HMB-45, desmin, smooth muscle actin, calponin, h-caldesmon, anaplastic lymphoma kinase, S-100 protein, epithelial membrane antigen, c-kit (CD117), stem cell factor (SCF/N19 or kit ligand), p53, bcl-2, cyclin D1, and human herpesvirus-8 (HHV8). In situ hybridization for Epstein-Barr virus-encoded RNA (EBER) was also performed. Ten cases were further evaluated for the dendritic cell markers fascin, CD21, CD23, and CD35. Stromal cells were diffusely positive for CD34 and fascin in all (100%) cases, and these stromal cells were, in addition, immunoreactive for calponin and smooth muscle actin in 88% and 25% of cases, respectively. CD35 was also found to be focally reactive in the stromal cells. Cyclin-D1 was overexpressed in all (100%) IFPs. All other immunohistochemical markers and EBER were negative in the stromal cells. These findings suggest that the proliferating stromal cells in IFPs are of dendritic cell origin, with some cases also exhibiting myofibroblastic features. Absence of c-kit, SCF, and h-caldesmon immunoreactivity fails to support a relationship to GISTs. We also conclude that Epstein Barr virus and HHV8 are unlikely etiologic agents of IFPs. Overexpression of cyclin D1 in all cases suggests that a defect in cell-cycle regulation may be involved in the growth of IFPs.

Common ALK gene rearrangement in Asian CD30+ anaplastic large cell lymphoma: an immunohistochemical and fluorescence in situ hybridisation (FISH) study on paraffin-embedded tissue

AIMS

The most common recurrent genetic aberration in anaplastic large cell lymphoma (ALCL) is translocation involving the ALK gene that results in ectopic expression of ALK protein in lymphoid tissue. This study aims to investigate the frequency of ALK gene rearrangement in a series of Asian ALCL.

METHODS

ALK gene rearrangement was detected by immunostaining of ALK protein and fluorescence in situ hybridisation (FISH) targeting at the 2p23 region.

RESULTS

The expression of ALK protein was detected in 24/34 (71%) of the cases, and it was significantly higher in childhood cases (100%) when compared to adult cases (47%). The analyses by FISH were consistent with the results from immunostaining of ALK protein, but the analyses were only successful in 15/34 (44%) cases. FISH analyses detected extra copies of ALK gene in three cases, including one case that expressed ALK protein and showed 2p23 rearrangement.

CONCLUSIONS

The current series revealed a high frequency of ALK gene rearrangement, especially in the children. Immunostaining of ALK protein is a reliable indication of ALK gene rearrangement, and is superior to FISH. However, FISH analysis is useful in detecting other genetic aberrations that are not related to ALK gene rearrangement.

A novel CLTC-TFE3 gene fusion in pediatric renal adenocarcinoma with t(X;17)(p11.2;q23)

A distinctive subset of renal carcinomas is associated with Xp11. 2 translocations and resulting TFE3 gene fusions (PRCC-TFE3, PSF-TFE3, NONO-TFE3, ASPL-TFE3), encoding related aberrant transcription factors. We report the cloning of a novel clathrin heavy-chain gene (CLTC)-TFE3 gene fusion resulting from a t(X;17)(p11.2;q23) in a renal carcinoma arising in a 14-year-old boy. The fusion transcript joined the 5' exons of CLTC on chromosome band 17q23 to the 3' exons of TFE3. CLTC encodes a major subunit of clathrin, a multimeric protein on cytoplasmic organelles, and is a known recurrent fusion partner of the ALK tyrosine kinase gene in anaplastic large-cell lymphoma and inflammatory myofibroblastic tumors. The predicted CLTC-TFE3 product retains the nuclear localization and DNA-binding domains of TFE3, but lacks the multimerization domain of CLTC. The present renal tumor demonstrated morphologic and immunohistochemical features of both PRCC-TFE3 and ASPL-TFE3 carcinomas, including strong nuclear immunoreactivity for the TFE3 C-terminal and only minimal expression of epithelial proteins. However, unlike most renal carcinomas, it also focally expressed melanocytic proteins. The present report highlights the promiscuity of certain genes involved in chromosomal translocations. Further analysis of the shared features of CLTC and other TFE3 fusion partners may shed light on the essential biology of TFE3 fusion proteins.

Practical application of molecular genetic testing as an aid to the surgical pathologic diagnosis of sarcomas: a prospective study

The strong correlation of specific reciprocal translocations with individual tumor types and the demonstration that polymerase chain reaction (PCR)-based methods can detect translocations in tissue samples have stimulated interest in the role of molecular genetic testing in diagnostic surgical pathology. To evaluate the clinical utility of PCR-based molecular analysis of soft tissue neoplasms in routine surgical pathology, 131 consecutive soft tissue tumors submitted for molecular genetic testing at a tertiary care teaching hospital were prospectively analyzed over a 36-month period. RT-PCR was used to test tumor RNA for fusion transcripts characteristic of malignant round cell tumors (including Ewing sarcoma/primitive neuroectodermal tumor, desmoplastic small round cell tumor, and alveolar rhabdomyosarcoma), spindle cell tumors (including synovial sarcoma and congenital fibrosarcoma), and fatty tumors (myxoid liposarcoma). DNA sequence analysis was used to confirm the identity of all PCR products, and the PCR results were compared with the histopathologic diagnosis. We found that sufficient RNA for RT-PCR-based testing was recovered from 96% of the 131 cases and the percentage of tumors that tested positive for the associated characteristic fusion transcript was in general agreement with those reported in the literature. DNA sequence analysis of PCR products identified both variant transcripts and spurious PCR products, underscoring the value of product confirmation steps when testing formalin-fixed, paraffin-embedded tissue. Only in rare cases did testing yield a genetic result that was discordant with the histopathologic diagnosis. We conclude that PCR-based testing is a useful adjunct for the diagnosis of malignant small round cell tumors, spindle cell tumors, and other miscellaneous neoplasms in routine surgical pathology practice.

Calcifying fibrous 'pseudotumor': clinicopathologic study of 15 cases and analysis of its relationship to inflammatory myofibroblastic tumor

Calcifying fibrous pseudotumor (CFP) has been postulated to be a "late" stage of inflammatory myofibroblastic tumor (IMT). We analyzed 15 cases (8 females and 7 males; aged 1 to 65 years). The anatomic distribution was wide, including 3 cases each in neck, mesentery/omentum, and GI tract and 2 cases each in mediastinum and paratesticular sites. Follow-up information was available in 10 patients (range 4 to 228 months). Local recurrence occurred in 3 patients and was repeated in 2. Tumor size ranged from 0.6 to 25 cm. Lesions were well-circumscribed hypocellular spindle cell proliferations with dense stromal collagen, a lymphoplasmacytic infiltrate, and stromal calcifications. Features of conventional IMT were not seen. Immunostaining showed CD34 positivity in most cases as well as rare cells positive for smooth muscle actin and desmin, and consistent negativity for ALK-1 and S-100 protein. These findings suggest that CFP is a distinctive benign mesenchymal neoplasm with a low risk for recurrence and, therefore, best labelled as "calcifying fibrous tumor." There is no convincing evidence to support an association between CFP and IMT.

Fusion tyrosine kinases induce drug resistance by stimulation of homology-dependent recombination repair, prolongation of G(2)/M phase, and protection from apoptosis

Fusion tyrosine kinases (FTKs) such as BCR/ABL, TEL/ABL, TEL/JAK2, TEL/PDGF beta R, TEL/TRKC(L), and NPM/ALK arise from reciprocal chromosomal translocations and cause acute and chronic leukemias and non-Hodgkin's lymphoma. FTK-transformed cells displayed drug resistance against the cytostatic drugs cisplatin and mitomycin C. These cells were not protected from drug-mediated DNA damage, implicating activation of the mechanisms preventing DNA damage-induced apoptosis. Various FTKs, except TEL/TRKC(L), can activate STAT5, which may be required to induce drug resistance. We show that STAT5 is essential for FTK-dependent upregulation of RAD51, which plays a central role in homology-dependent recombinational repair (HRR) of DNA double-strand breaks (DSBs). Elevated levels of Rad51 contributed to the induction of drug resistance and facilitation of the HRR in FTK-transformed cells. In addition, expression of antiapoptotic protein Bcl-xL was enhanced in cells transformed by the FTKs able to activate STAT5. Moreover, cells transformed by all examined FTKs displayed G(2)/M delay upon drug treatment. Individually, elevated levels of Rad51, Bcl-xL, or G(2)/M delay were responsible for induction of a modest drug resistance. Interestingly, combination of these three factors in nontransformed cells induced drug resistance of a magnitude similar to that observed in cells expressing FTKs activating STAT5. Thus, we postulate that RAD51-dependent facilitation of DSB repair, antiapoptotic activity of Bcl-xL, and delay in progression through the G(2)/M phase work in concert to induce drug resistance in FTK-positive leukemias and lymphomas.

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.

Differential expression of BCL-2 family proteins in ALK-positive and ALK-negative anaplastic large cell lymphoma of T/null-cell lineage

Anaplastic large-cell lymphoma (ALCL) of T- or null-cell lineage, as defined in the revised European-American lymphoma classification, includes a subset of tumors that carry the t(2;5)(p23;q35) resulting in overexpression of anaplastic lymphoma kinase (ALK). Patients with ALK+ ALCL are reported to have a better prognosis than patients with ALK- ALCL. Because the mechanisms for this survival difference are unknown, we investigated the hypothesis that apoptotic pathways may be involved. We therefore assessed expression levels of the anti-apoptotic proteins BCL-2 and BCL-XL and the pro-apoptotic proteins BAX and BCL-XS in T/null-cell ALCL using immunohistochemical methods and correlated the findings with ALK expression and apoptotic rate (AR), the latter assessed by a modified Tdt-mediated dUTP nick-end labeling assay. ALK was detected in 21 of 66 (31.8%) ALCLs. BCL-2 was not detected in 21 ALK+ ALCLs but was present in 26 of 45 (57.8%) ALK- ALCLs (P < 0.0001). ALK+ and ALK- ALCLs also showed significant differences in expression of BCL-XL, BAX, and BCL-XS. ALK+ tumors less commonly had a high level of BCL-XL (1 of 17 versus 14 of 35, P = 0.01), and more commonly had high levels of BAX (13 of 18 versus 15 of 36, P = 0.05), and BCL-XS (11 of 16 versus 12 of 31, P = 0.05) compared with ALK- tumors. ALK+ tumors also had a higher mean AR than ALK- tumors (3.4% versus 1.1%, P = 0.0002). Differential expression of BCL-2 family proteins may be responsible for the higher AR observed in ALK+ ALCL and provides a possible biological explanation for the better prognosis reported for patients with ALK+ ALCL.

Recent progress in the classification of soft tissue tumors: role of genetics and clinical implications

Soft tissue tumors comprise a vast and heterogeneous group of neoplasms. Because different tumors often have different biological behaviors and respond differently to various therapeutic modalities, precise classification is paramount. The majority of soft tissue tumors were first delineated on the basis of morphologic and clinical findings, which in many cases were adequate to accurately separate different tumors into homogeneous groups; however, it has increasingly been appreciated that many entities are actually heterogeneous groups of tumors that have similar histologic and pathologic characteristics but differ in their clinical behavior and underlying pathogenesis. Within the past several years, great strides have been made in the purification of different entities. This accomplishment has largely been because of advances in our understanding of the molecular genetics that underlie the pathogenesis of many sarcomas and the development of new and specific tumor markers. This review highlights some important recent work in two selected soft tissue tumors-gastrointestinal stromal tumor and inflammatory myofibroblastic tumor. These examples illustrate the type of progress that is being made in the classification of soft tissue tumors.

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.

Human herpesvirus-8 genes are expressed in pulmonary inflammatory myofibroblastic tumor (inflammatory pseudotumor)

The presence of human herpesvirus-8 DNA sequences, as well as an overexpression of human interleukin-6 and human cyclin D1 in myofibroblastic cells of inflammatory myofibroblastic tumor (inflammatory pseudotumor), has recently been reported. We describe the pattern of human herpesvirus-8 gene expression in five cases of pulmonary inflammatory myofibroblastic tumor. Reverse transcriptase-polymerase chain reaction (RT-PCR), with several positive and negative controls, was performed to detect mRNA of 11 open reading frames encoded by human herpesvirus-8 in lytic and latent stages of viral replicative cycle. We found molecular transcripts from ORF16, ORFK13, and ORF72 in the five cases and from ORFK2 in four of five neoplasms. The corresponding encoded proteins were human homologous oncoproteins (viral cyclin-D), inflammatory cytokines (viral IL-6), and inhibitors of apoptotic pathways (viral FLIP and viral Bcl-2), mostly expressed in a latent viral replicative stage. The rest of open reading frames examined included mainly lytic-associated genes and showed no expression. The spectrum of expressed viral genes is not the same as can be observed in Kaposi's sarcoma or multicentric Castleman's disease, suggesting that human herpesvirus-8 plays a different role in the pathogenesis of its associated diseases. These differences may be related to either cell-specific or immunologic host factors.

The protein tyrosine kinase family of the human genome

As the sequencing of the human genome is completed by the Human Genome Project, the analysis of this rich source of information will illuminate many areas in medicine and biology. The protein tyrosine kinases are a large multigene family with particular relevance to many human diseases, including cancer. A search of the human genome for tyrosine kinase coding elements identified several novel genes and enabled the creation of a nonredundant catalog of tyrosine kinase genes. Ninety unique kinase genes can be identified in the human genome, along with five pseudogenes. Of the 90 tyrosine kinases, 58 are receptor type, distributed into 20 subfamilies. The 32 nonreceptor tyrosine kinases can be placed in 10 subfamilies. Additionally, mouse orthologs can be identified for nearly all the human tyrosine kinases. The completion of the human tyrosine kinase family tree provides a framework for further advances in biomedical science.