POU5F1 , encoding a key regulator of stem cell pluripotency, is fused to EWSR1 in hidradenoma of the skin and mucoepidermoid carcinoma of the salivary glands

Psoriasis regression analysis of MHC loci identifies shared genetic variants with vitiligo

Psoriasis is a common inflammatory skin disease with genetic components of both immune system and the epidermis. PSOR1 locus (6q21) has been strongly associated with psoriasis; however, it is difficult to identify additional independent association due to strong linkage disequilibrium in the MHC region. We performed stepwise regression analyses of more than 3,000 SNPs in the MHC region genotyped using Human 610-Quad (Illumina) in 1,139 cases with psoriasis and 1,132 controls of Han Chinese population to search for additional independent association. With four regression models obtained, two SNPs rs9468925 in HLA-C/HLA-B and rs2858881 in HLA-DQA2 were repeatedly selected in all models, suggesting that multiple loci outside PSOR1 locus were associated with psoriasis. More importantly we find that rs9468925 in HLA-C/HLA-B is associated with both psoriasis and vitiligo, providing first important evidence that two major skin diseases share a common genetic locus in the MHC, and a basis for elucidating the molecular mechanism of skin disorders.

EWSR1 gene rearrangement occurs in a subset of cutaneous myoepithelial tumors: a study of 18 cases

Cutaneous myoepithelial tumors form a clinicopathological spectrum ranging from mixed tumor to myoepithelioma and myoepithelial carcinoma. Recently, EWSR1 rearrangement has been described in a subset of soft tissue myoepithelial tumors, whereas the cutaneous counterparts showed this aberration in a minority of cases. This raises the question whether cutaneous myoepithelial tumors have comparable genetic alterations. We examined 18 cases of cutaneous myoepithelial tumors arising in 7 female and 11 male patients (age range, 34-86 years; mean, 58 years). Eight mixed tumors occurred at the head, and one at the scrotum. Six myoepitheliomas arose at the extremities, and one case each at the back and head. One myoepithelial carcinoma occurred at the cheek. The tumor size ranged from 0.3 to 1.7 cm (mean, 1.0 cm). All mixed tumors and three myoepitheliomas were limited to the dermis. Four myoepitheliomas and the myoepithelial carcinoma involved the subcutis. Mixed tumors and myoepitheliomas were composed of myoepithelial cells with a variable cytomorphology, architecture and stromal background. Ductal structures were seen by definition in mixed tumors. The myoepithelial carcinoma represented an infiltrative dermal neoplasm consisting of atypical spindle cells. Immunohistochemically, all cases tested were positive for EMA and calponin, whereas S100, CK, ASMA and GFAP were expressed in 90%, 80%, 78% and 50% of the cases tested, respectively. By fluorescent in situ hybridization analysis, 7 out of 16 cases (44%) exhibited EWSR1 rearrangement. Four of them were mixed tumors, two were myoepitheliomas and one was a myoepithelial carcinoma, confirming that these lesions represent a spectrum of dermal myoepithelial tumors. Follow-up information, available for five patients (including the patient with a myoepithelial carcinoma), revealed no evidence of disease in all cases (range, 6-72 months). Our study provides a genetic relationship of myoepithelial tumors of the skin with their counterparts in soft tissue, bone and visceral localization by sharing EWSR1 rearrangement.

A subset of cutaneous and soft tissue mixed tumors are genetically linked to their salivary gland counterpart

Neoplasms morphologically similar to mixed tumors and myoepitheliomas of the salivary glands, under the broad concept of myoepithelial neoplasia, have recently been defined in the skin and soft tissue; however, to date, no data have supported a shared genetic background with their salivary gland counterpart. From a large body of research, it has been well established that rearrangement of pleomorphic adenoma gene 1 (PLAG1) leads to aberrant expression of its protein and is pathogenically relevant in the development of salivary mixed tumors. On the other hand, in soft tissue lesions, compelling evidence suggests that EWSR1 is involved in a significant subset. To examine the hypothesis that there is a genetic link between these histologically similar tumors at different sites, we randomly selected 20 benign myoepitheliomas/mixed tumors of skin and soft tissue (10 cases each). Nineteen cases could be immunostained for PLAG1, of which 11 cases showed distinct nuclear staining with moderate or strong intensity in a significant number of cells. Interphase fluorescence in situ hybridization for PLAG1 was successfully performed in 11 cases (seven in skin and four in soft tissue) and was positive for gene rearrangement in eight cases (five in skin and three in soft tissue). All PLAG1-rearranged tumors, except one, had clear-cut ductal structures and were immunoreactive for PLAG1. In our series, tumors with PLAG1 alteration shared a common morphologic phenotype characterized by prominent tubuloductal differentiation, suggesting that myoepithelial neoplasms with genuine salivary gland-like morphology, so-called soft tissue/cutaneous mixed tumors, are genetically related to their salivary gland counterpart.

Molecular pathogenesis of Ewing sarcoma: new therapeutic and transcriptional targets

Approximately one-third of sarcomas contain specific translocations. Ewing sarcoma is the prototypical member of this group of sarcomas; it was the first to be recognized pathologically as a singular entity and to have its signature translocation defined cytogenetically, which led to the identification of its key driver alteration, the EWS-FLI1 gene fusion that encodes this aberrant, chimeric transcription factor. We review recent progress in selected areas of Ewing sarcoma research, including the application of genome-wide chromatin immunoprecipitation analyses, to provide a comprehensive view of the EWS-FLI1 target gene repertoire, the identification of EWS-FLI1 target genes that may also point to therapeutically targetable pathways, and data from model systems as they relate to the elusive cell of origin of Ewing sarcoma and its possible similarities to mesenchymal stem cells.

Advances in sarcoma genomics and new therapeutic targets

Increasingly, human mesenchymal malignancies are being classified by the abnormalities that drive their pathogenesis. Although many of these aberrations are highly prevalent within particular sarcoma subtypes, few are currently targeted therapeutically. Indeed, most subtypes of sarcoma are still treated with traditional therapeutic modalities, and in many cases sarcomas are resistant to adjuvant therapies. In this Review, we discuss the core molecular determinants of sarcomagenesis and emphasize the emerging genomic and functional genetic approaches that, coupled with novel therapeutic strategies, have the potential to transform the care of patients with sarcoma.

The MYB-NFIB gene fusion-a novel genetic link between adenoid cystic carcinoma and dermal cylindroma

We have recently shown that the recurrent t(6;9)(q22 ∼ 23;p23 ∼ 24) translocation in adenoid cystic carcinoma (ACC) of the breast and head and neck results in a fusion of the two transcription factor genes MYB and NFIB. Here we demonstrate, for the first time, that benign sporadic, dermal cylindromas also express the MYB-NFIB gene fusion. RT-PCR and immunohistochemical analyses revealed that eight of 12 analysed tumours (67%) expressed MYB-NFIB fusion transcripts and/or stained positive for MYB protein. Nucleotide sequence analyses confirmed that the composition of the chimeric transcript variants identified was identical to that in ACC, suggesting a similar molecular mechanism of activation of MYB in cylindroma as in ACC. In contrast, no evidence for the presence of the MYB-NFIB fusion was found in other types of basaloid skin and salivary gland tumours, indicating that the fusion indeed has a restricted expression pattern. Our findings broaden the spectrum of neoplasms associated with MYB oncogene activation and reveal a novel genetic link between ACC and dermal cylindroma. These results, together with our previous observations, further strengthen the evidence for common molecular pathways of importance for the development of both benign and malignant breast, salivary and adnexal tumours.

MED19 promotes proliferation and tumorigenesis of lung cancer

MED19 is a subunit of Mediator that is an essential component of RNA polymerase II-mediated transcription machinery. High expression levels of MED19 were examined in human lung adenocarcinoma tissues by immunohistochemical assay. MED19-specific short hairpin RNA (shRNA) expressing lentivirus was constructed and infected lung cancer cell line A549. MED19 mRNA and protein expression levels were downregulated in A549 cells as evidenced by real-time PCR and western blot assays. Importantly, MED19 inhibition resulted in impaired proliferation and colony formation, and induced accumulation of G1-phase cells and mitigated invasiveness of cells. More importantly, downregulation of MED19 expression reduced the tumorigenicity of A549 cells in vivo. It was suggested that MED19 is a novel proliferation regulator that promotes growth of lung cancer cells, thereby indicating that MED19 may serve as a new molecular target for lung cancer therapy.

EWSR1-ATF1 fusion is a novel and consistent finding in hyalinizing clear-cell carcinoma of salivary gland

Hyalinizing clear-cell carcinoma (HCCC) is a rare, low-grade salivary gland tumor with distinctive clear-cell morphology and pattern of hyalinization as well as focal mucinous differentiation. However, histological overlap exists with other salivary gland tumors, such as epithelial-myoepithelial carcinoma (EMCa), salivary myoepithelial carcinoma, and mucoepidermoid carcinoma (MEC). The potential relationship between HCCC and its morphological mimics has not been yet investigated at the genetic level. In this study, we conducted a molecular analysis for the presence of rearrangements in MAML2, commonly seen in MECs, and EWSR1, involved in "soft tissue myoepithelial tumors" (SMET) by fusion with POU5F1, PBX1, or ZNF444. Fluorescence in situ hybridization (FISH) was performed on 23 HCCC cases for abnormalities in MAML2, EWSR1, FUS, POU5F1, PBX1, and ZNF444. FISH for MAML2 was negative in all cases (0 of 14), including those with mucinous differentiation (0 of 7). An EWSR1 rearrangement was identified in 18 of 22 HCCCs (82%), while no break-apart signals were seen in FUS, POU5F1, PBX1, or ZNF444. 3'RACE on an EWSR1 rearranged HCCC identified an EWSR1-ATF1 fusion, which was confirmed by RT-PCR. ATF1 involvement was further confirmed by FISH analysis in 13 of 14 EWSR1-rearranged HCCC cases (93%). In contrast, all control cases tested, including among others 5 EMCa and 3 MEC with clear cells, were negative for EWSR1 and ATF1 rearrangements. The presence of EWSR1-ATF1 fusion in most HCCCs reliably separates these tumors from its histological mimics. The distinction from MEC is particularly important, as conventional MEC grading schemes overgrade these indolent HCCCs, potentially impacting on treatment.

Dr. Jekyll and Mr. Hyde: The Two Faces of the FUS/EWS/TAF15 Protein Family

FUS, EWS, and TAF15 form the FET family of RNA-binding proteins whose genes are found rearranged with various transcription factor genes predominantly in sarcomas and in rare hematopoietic and epithelial cancers. The resulting fusion gene products have attracted considerable interest as diagnostic and promising therapeutic targets. So far, oncogenic FET fusion proteins have been regarded as strong transcription factors that aberrantly activate or repress target genes of their DNA-binding fusion partners. However, the role of the transactivating domain in the context of the normal FET proteins is poorly defined, and, therefore, our knowledge on how FET aberrations impact on tumor biology is incomplete. Since we believe that a full understanding of aberrant FET protein function can only arise from looking at both sides of the coin, the good and the evil, this paper summarizes evidence for the central function of FET proteins in bridging RNA transcription, processing, transport, and DNA repair.

EWSR1-POU5F1 fusion in soft tissue myoepithelial tumors. A molecular analysis of sixty-six cases, including soft tissue, bone, and visceral lesions, showing common involvement of the EWSR1 gene

The diagnosis of myoepithelial (ME) tumors outside salivary glands remains challenging, especially in unusual clinical presentations, such as bone or visceral locations. A few reports have indicated EWSR1 gene rearrangement in soft tissue ME tumors, and, in one case each, the fusion partner was identified as either PBX1 or ZNF444. However, larger studies to investigate whether these genetic abnormalities are recurrent or restricted to tumors in soft tissue locations are lacking. Sixty-six ME tumors mainly from soft tissue (71%), but also from skin, bone, and visceral locations, characterized by classic morphological features and supporting immunoprofile were studied. Gene rearrangements in EWSR1, FUS, PBX1, and ZNF444 were investigated by fluorescence in situ hybridization. EWSR1 gene rearrangement was detected in 45% of the cases. A EWSR1-POU5F1 fusion was identified in a pediatric soft tissue tumor by 3'Rapid Amplification of cDNA Euds (RACE) and subsequently confirmed in four additional soft tissue tumors in children and young adults. An EWSR1-PBX1 fusion was seen in five cases, whereas EWSR1-ZNF444 and FUS gene rearrangement was noted in one pulmonary tumor each. In conclusion, EWSR1 gene rearrangement is a common event in ME tumors arising outside salivary glands, irrespective of anatomical location. EWSR1-negative tumors were more often benign, superficially located, and showed ductal differentiation, suggesting the possibility of genetically distinct groups. A subset of soft tissue ME tumors with clear cell morphology harbor an EWSR1-POU5F1 fusion, which can be used as a molecular diagnostic test in difficult cases. These findings do not support a pathogenetic relationship between soft tissue ME tumors and their salivary gland counterparts.

New tricks from an old oncogene: gene fusion and copy number alterations of MYB in human cancer

MYB is a leucine zipper transcription factor that is essential for hematopoesis and for renewal of colonic crypts. There is also ample evidence showing that MYB is leukemogenic in several animal species. However, it was not until recently that clear evidence was presented showing that MYB actually is an oncogene rearranged in human cancer. In a recent study, a novel mechanism of activation of MYB involving gene fusion was identified in carcinomas of the breast and head and neck. A t(6;9) translocation was shown to generate fusions between MYB and the transcription factor gene NFIB. The fusions consistently result in loss of the 3'-end of MYB, including several highly conserved target sites for microRNAs that negatively regulate MYB expression. Deletion of these target sites may disrupt the repression of MYB, leading to overexpression of MYB-NFIB transcripts and protein and to transcriptional activation of critical MYB target genes associated with apoptosis, cell cycle control, cell growth/angiogenesis and cell adhesion. This study, together with previous and recent data showing rearrangements and copy number alterations of the MYB locus in T-cell leukemia and certain solid tumors, will be the main focus of this review.

Genotypic and phenotypic classification of cancer: How should the impact of the two diagnostic approaches best be balanced?

Neoplastic tumors are traditionally named based on their differentiation (i.e., which normal cells and tissues they resemble) and bodily site. In recent years, knowledge about the genetic basis of tumorigenesis has grown rapidly, and the new information has in several instances been incorporated into the very definition of cancerous entities. The proper contribution of the diseases' phenotype and genotype to what they are called and how they are delineated from one another has rarely been subjected to explicit reasoning, however, nor is it often made clear whether existing naming practices are founded on ontological or utilitarian grounds. We look at several examples of how the new cytogenetic and molecular genetic understanding of tumorigenesis has impacted oncological nomenclature in a significant manner, but also at counterexamples where no similar change has taken place. In all likelihood, more and more neoplastic diseases will in the future be defined and named based on their pathogenesis rather than their phenotype, not least because effective and specific drug therapies directed against the molecular change at the very heart of oncogenesis will increasingly become available. The fact that this shift in emphasis is primarily guided by utilitarian considerations rather than any perception of acquired genetic changes as somehow being more ontologically "profound" or "important" in tumorigenesis, is as it should be; both the phenotype and the genotype of tumors are key parameters across most of oncology and are likely to be retained as the basis of coexisting disease classifications for as long as we can foresee.

POU5F1P1, a putative cancer susceptibility gene, is overexpressed in prostatic carcinoma

BACKGROUND

Association between genetic variants located on human chromosome 8q24.21 with an increased risk for prostatic carcinoma has been well established. POU5F1P1, a processed pseudogene homologous to the pluripotency factor OCT4, is the only sequence with coding capacity in this region. The objective of this study was to investigate the POU5F1P1 expression in prostatic carcinoma and carcinoma surrounding prostatic tissue.

METHODS

RT-PCR and real-time PCR was used to measure the expression of POU5F1P1 relative to the expression of HPRT1 in cell lines, prostatic carcinoma and carcinoma surrounding prostatic tissue. The structure of the POU5F1P1 mRNA and the promoter sequence were elucidated by 5'-RACE experiments. The POU5F1P1 protein was shown with immunohistochemistry on prostate tissue.

RESULTS

POU5F1P1 was found to be the only member of the POU5F1 family to be expressed in prostate with over-expression in prostatic carcinoma compared to surrounding prostatic tissue probably because of an increased density of expressing cells. The POU5F1P1 expression is driven by a variety of promoter structures scattered over a genomic region of 860 kB.

CONCLUSIONS

The over-expression of POU5F1P1 in prostatic carcinoma in addition to its genomic location and the putative function of its gene product render POU5F1P1 a good candidate to harbour functional genetic variants which modulate prostatic cancer susceptibility.

Soft tissue tumors associated with EWSR1 translocation

The Ewing sarcoma breakpoint region 1 (EWSR1; also known as EWS) represents one of the most commonly involved genes in sarcoma translocations. In fact, it is involved in a broad variety of mesenchymal lesions which includes Ewing's sarcoma/peripheral neuroectodermal tumor, desmoplastic small round cell tumor,clear cell sarcoma, angiomatoid fibrous histiocytoma, extraskeletal myxoid chondrosarcoma, and a subset of myxoid liposarcoma. The fusion products between EWSR1 and partners usually results in fusion of the N-terminal transcription-activating domain of EWSR1 and the C-terminal DNA-binding domain of the fusion partner, eventually generating novel transcription factors. EWSR1 rearrangement can be visualized by the means of fluorescence in situ hybridization (FISH). As soft tissue sarcomas represent a diagnostically challenging group, FISH analysis is an extremely useful confirmatory diagnostic tool. However, as in most instances a split-apart approach is used, the results of molecular genetics must be evaluated in context with morphology.

Function of EWS-POU5F1 in sarcomagenesis and tumor cell maintenance

POU5F1 is a transcription factor essential for the self-renewal activity and pluripotency of embryonic stem cells and germ cells. We have previously reported that POU5F1 is fused to EWSR1 in a case of undifferentiated sarcoma with chromosomal translocation t(6;22)(p21;q12). In addition, the EWS-POU5F1 chimeras have been recently identified in human neoplasms of the skin and salivary glands. To clarify the roles of the EWS-POU5F1 chimera in tumorigenesis and tumor cell maintenance, we used small-interfering RNA-mediated gene silencing. Knockdown of EWS-POU5F1 in the t(6;22) sarcoma-derived GBS6 cell line resulted in a significant decrease of cell proliferation because of G1 cell cycle arrest associated with p27(Kip1) up-regulation. Moreover, senescence-like morphological changes accompanied by actin polymerization were observed. In contrast, EWS-POU5F1 down-regulation markedly increased the cell migration and invasion as well as activation of metalloproteinase 2 and metalloproteinase 14. The results indicate that the proliferative activity of cancer cells and cell motility are discrete processes in multistep carcinogenesis. These findings reveal the functional role of the sarcoma-related chimeric protein as well as POU5F1 in the development and progression of human neoplasms.

EWS-Oct-4B, an alternative EWS-Oct-4 fusion gene, is a potent oncogene linked to human epithelial tumours

BACKGROUND

Characterisation of EWS-Oct-4 translocation fusion product in bone and soft-tissue tumours revealed a chimeric gene resulting from an in-frame fusion between EWS (Ewing's sarcoma gene) exons 1-6 and Oct-4 exons 1-4. Recently, an alternative form of the fusion protein between the EWS and Oct-4 genes, named EWS-Oct-4B, was reported in two types of epithelial tumours, a hidradenoma of the skin and a mucoepidermoid carcinoma of the salivary glands. As the N-terminal and POU domains of the EWS-Oct-4 and EWS-Oct-4B proteins are not structurally identical, we decided to investigate the functional consequences of the EWS-Oct-4B fusion.

METHODS

In this report, we have characterised the EWS-Oct-4B fusion protein. To investigate how the EWS-Oct-4B protein contributes to tumourigenesis in human cancers, we analysed its DNA-binding activity, subcellular localisation, transcriptional activation behaviour, and oncogenic properties.

RESULTS

We found that this new chimeric gene encodes a nuclear protein that binds DNA with the same sequence specificity as the parental Oct-4 protein or the fusion EWS-Oct-4 protein. We show that the nuclear localisation signal of EWS-Oct-4B is dependent on the POU DNA-binding domain, and we identified a cluster of basic amino acids, (269)RKRKR(273), in the POU domain that specifically mediates the nuclear localisation of EWS-Oct-4B. Comparison of the properties of EWS-Oct-4B and EWS-Oct-4 indicated that EWS-Oct-4B is a less-potent transcriptional activator of a reporter construct carrying the Oct-4-binding sites. Deletion analysis of the functional domains of EWS-Oct-4B revealed that the EWS N-terminal domain (NTD)(B), POU, and C-terminal domain (CTD) are necessary for its full transactivation potential. Despite its reduced activity as a transcriptional activator, EWS-Oct-4B regulated the expression of fgf-4 (fibroblast growth factor-4) and nanog, which are potent mitogens, as well as of Oct-4 downstream target genes, the promoters of which contain potential Oct-4-binding sites. Finally, ectopic expression of EWS-Oct-4B in Oct-4-null ZHBTc4 ES cells resulted in increased tumourigenic growth potential in nude mice.

CONCLUSION

These results suggest that the oncogenic effect of the t(6;22) translocation is due to the EWS-Oct-4B chimeric protein, and that alternative fusion of the EWS amino terminal domain to the Oct-4 DNA-binding domain produces another transforming chimeric product in human epithelial tumours.

t(19;22)(q13;q12) Translocation leading to the novel fusion gene EWSR1-ZNF444 in soft tissue myoepithelial carcinoma

Myoepithelial neoplasms of soft tissue have only recently been acknowledged as a separate diagnostic entity. To know based on histological appearance whether these tumors are benign or malignant is often difficult, and their tumorigenic mechanisms remain poorly understood. We report a myoepithelial carcinoma with an aberrant near-diploid karyotype, 43 approximately 47,XX,add(1)(p34)x2,add(3)(q27)x2,del(12)(q22),+add(18)(p11)x2,del(22)(q11),+r, found in cells cultured from a lung metastasis. The deletion in 22q led us to search by molecular cytogenetic means for possible EWSR1 rearrangements, and eventually a novel chimeric gene consisting of the 5'-end of EWSR1 (22q12) and the 3'-end of ZNF444 (19q13) was found. How the new fusion gene contributes to tumorigenesis is unknown, but the finding of an EWSR1 rearrangement suggests that this, possibly even the EWSR1-ZNF444, is a defining pathogenetic feature of at least a subset of these tumors.

Human testicular (non)seminomatous germ cell tumours: the clinical implications of recent pathobiological insights

Human germ cell tumours (GCTs) comprise several types of neoplasias with different pathogeneses and clinical behaviours. A classification into five subtypes has been proposed. Here, the so-called type II testicular GCTs (TGCTs), ie the seminomas and non-seminomas, will be reviewed with emphasis on pathogenesis and clinical implications. Various risk factors have been identified that define subpopulations of men who are amenable to early diagnosis. TGCTs are omnipotent, able to generate all differentiation lineages, both embryonic and extra-embryonic, as well as the germ cell lineage itself. The precursor lesion, composed of primordial germ cells/gonocytes, is referred to as carcinoma in situ of the testis (CIS) and gonadoblastoma of the dysgenetic gonad. These pre-malignant cells retain embryonic characteristics, which probably explains the unique responsiveness of the derived tumours to DNA-damaging agents. Development of CIS and gonadoblastoma is crucially dependent on the micro-environment created by Sertoli cells in the testis, and granulosa cells in the dysgenetic gonad. OCT3/4 has high sensitivity and specificity for CIS/gonadoblastoma, seminoma, and embryonal carcinoma, and is useful for the detection of CIS cells in semen, thus a promising tool for non-invasive screening. Overdiagnosis of CIS due to germ cell maturation delay can be avoided using immunohistochemical detection of stem cell factor (SCF). Immunohistochemistry is helpful in making the distinction between seminoma and embryonal carcinoma, especially SOX17 and SOX2. The different non-seminomatous histological elements can be recognized using various markers, such as AFP and hCG, while others need confirmation. The value of micro-satellite instability as well as BRAF mutations in predicting treatment resistance needs validation in prospective trials. The availability of representative cell lines, both for seminoma and for embryonal carcinoma, allows mechanistic studies into the initiation and progression of this disease.

Mutation-associated fusion cancer genes in solid tumors

Chromosomal translocations and fusion oncogenes serve as the ultimate biomarker for clinicians as they show specificity for distinct histopathologic malignancies while simultaneously encoding an etiologic mutation and a therapeutic target. Previously considered a minor mutational event in epithelial solid tumors, new methodologies that do not rely on the detection of macroscopic cytogenetic alterations, as well as access to large series of annotated clinical material, are expanding the inventory of recurrent fusion oncogenes in both common and rare solid epithelial tumors. Unexpectedly, related assays are also revealing a high number of tandem or chimeric transcripts in normal tissues including, in one provocative case, a template for a known fusion oncogene. These observations may force us to reassess long-held views on the definition of a gene. They also raise the possibility that some rearrangements might represent constitutive forms of a physiological chimeric transcript. Defining the chimeric transcriptome in both health (transcription-induced chimerism and intergenic splicing) and disease (mutation-associated fusion oncogenes) will play an increasingly important role in the diagnosis, prognosis, and therapy of patients with cancer.