Analysis of MAML2 rearrangement in mucoepidermoid carcinoma of the thymus

Primary thymic mucoepidermoid carcinoma (TMEC) is rare. High-grade TMEC can be difficult to distinguish from poorly differentiated squamous cell carcinoma and adenosquamous carcinoma. A strong association between mucoepidermoid carcinoma (MEC) and t(11;19)(q21;p13) has been observed in other anatomical sites. Although this translocation is largely considered a disease-defining event for MEC, its incidence in TMEC has not been explored. In this study, we evaluate the value of identifying MAML2 rearrangement by fluorescence in situ hybridization (FISH) to distinguish TMEC from poorly differentiated squamous cell carcinoma and adenosquamous carcinoma. Cases of TMEC, moderate to poorly differentiated squamous cell carcinoma, and adenosquamous carcinoma were re-reviewed by 3 surgical pathologists and classified according to the current World Health Organization classification of thymic tumors (2004). Cases of TMEC were histologically graded using the Brandwein system. FISH was used to detect MAML2 rearrangements using a break-apart probe. FISH for MAML2 rearrangement was performed on cases of TMEC (n = 2), thymic squamous cell carcinoma (n = 5), and thymic adenosquamous carcinoma (n = 3). The 2 cases of TMEC showed MAML2 rearrangement. All other tested cases did not show rearrangement of MAML2. In conclusion, using FISH to identify MAML2 rearrangement is a valuable diagnostic tool in the evaluation of thymic malignancies, specifically, distinguishing TMEC from squamous cell carcinoma and adenosquamous carcinoma. These findings also suggest that TMEC has both histomorphologic and cytogenetic similarities to cases of MEC arising from other anatomical sites.

Fusion of dynactin 1 to anaplastic lymphoma kinase in inflammatory myofibroblastic tumor

Inflammatory myofibroblastic tumor is an uncommon neoplasm that occurs more often in younger patients. Approximately 50% of inflammatory myofibroblastic tumors are characterized by anaplastic lymphoma kinase fusion genes, more commonly TPM3-anaplastic lymphoma kinase and TPM4-anaplastic lymphoma kinase. Herein, we report a novel fusion of dynactin 1 to anaplastic lymphoma kinase in a neck inflammatory myofibroblastic tumor diagnosed in a 7-year-old girl. Histologic evaluation showed a perineurioma-like bland spindle cell neoplasm with positive immunohistochemical staining for anaplastic lymphoma kinase, S-100, and CD34 but negative for epithelial membrane antigen. Standard cytogenetic analysis showed a der(2)t(2;12)(p23;q11). Fluorescence in situ hybridization demonstrated separation of the anaplastic lymphoma kinase locus. 5'-rapid amplification of complementary DNA ends polymerase chain reaction identified an in-frame fusion of dynactin 1 exon 16 on chromosome 2 to anaplastic lymphoma kinase exon 20. Reverse transcription-polymerase chain reaction with specific primers and direct sequencing confirmed the fusion. The structure of the fusion protein retains the cytoskeleton-associated protein-glycine domain and coiled coil domain of dynactin 1 and the receptor tyrosine kinase domain of anaplastic lymphoma kinase. This novel fusion gene is structurally similar to other previously described anaplastic lymphoma kinase fusion genes and may be associated with the unusual morphology and immunophenotype of this tumor.

Nodular fasciitis: a novel model of transient neoplasia induced by MYH9-USP6 gene fusion

Nodular fasciitis (NF) is a relatively common mass-forming and self-limited subcutaneous pseudosarcomatous myofibroblastic proliferation of unknown pathogenesis. Due to its rapid growth and high mitotic activity, NF is often misdiagnosed as a sarcoma. While studying the USP6 biology in aneurysmal bone cyst and other mesenchymal tumors, we identified high expression levels of USP6 mRNA in two examples of NF. This finding led us to further examine the mechanisms underlying USP6 overexpression in these lesions. Upon subsequent investigation, genomic rearrangements of the USP6 locus were found in 92% (44 of 48) of NF. Rapid amplification of 5'-cDNA ends identified MYH9 as the translocation partner. RT-PCR and direct sequencing revealed the fusion of the MYH9 promoter region to the entire coding region of USP6. Control tumors and tissues were negative for this fusion. Xenografts of cells overexpressing USP6 in nude mice exhibited clinical and histological features similar to human NF. The identification of a sensitive and specific abnormality in NF holds the potential to be used diagnostically. Considering the self-limited nature of the lesion, NF may represent a model of 'transient neoplasia', as it is, to our knowledge, the first example of a self-limited human disease characterized by a recurrent somatic gene fusion event.

Identification of a disease-defining gene fusion in epithelioid hemangioendothelioma

Integrating transcriptomic sequencing with conventional cytogenetics, we identified WWTR1 (WW domain-containing transcription regulator 1) (3q25) and CAMTA1 (calmodulin-binding transcription activator 1) (1p36) as the two genes involved in the t(1;3)(p36;q25) chromosomal translocation that is characteristic of epithelioid hemangioendothelioma (EHE), a vascular sarcoma. This WWTR1/CAMTA1 gene fusion is under the transcriptional control of the WWTR1 promoter and encodes a putative chimeric transcription factor that joins the amino terminus of WWTR1, a protein that is highly expressed in endothelial cells, in-frame to the carboxyl terminus of CAMTA1, a protein that is normally expressed only in brain. Thus, CAMTA1 expression is activated inappropriately through a promoter-switch mechanism. The gene fusion is present in virtually all EHEs tested but is absent from all other vascular neoplasms, demonstrating it to be a disease-defining genetic alteration. A sensitive and specific break-apart fluorescence in situ hybridization assay was also developed to detect the translocation and will assist in the evaluation of this diagnostically challenging neoplasm. The chimeric WWTR1/CAMTA1 transcription factor may represent a therapeutic target for EHE and offers the opportunity to shed light on the functions of two poorly characterized proteins.

Fusion of HMGA2 to COG5 in uterine leiomyoma

Uterine leiomyomas are smooth muscle tumors most commonly seen in middle-aged women. Approximately 10% of these tumors contain rearrangements of the chromatin-remodeling gene HMGA2 at the chromosome band 12q14.3. Herein, we report on a uterine leiomyoma with a novel HMGA2 fusion gene. A 44-year-old woman presented with a 20-cm mass uterine leiomyoma. From a histological standpoint, the tumor exhibited extensive hyalinization, very low mitotic activity (<1/10 HPH), and no cytologic atypia. Smooth muscle differentiation was confirmed by the expression of smooth muscle actin and desmin. Standard cytogenetic analysis showed the reciprocal translocation t(7;12)(q31.2;q14.3). Fluorescence in situ hybridization analysis confirmed a balanced rearrangement of the HMGA2 locus in 80% of the cells. 3'RACE reverse-transcription polymerase chain reaction identified the fusion of HMGA2 exon 4 to the COG5 locus on 7q31 (component of oligomeric golgi complex 5 isoform). The fusion sequence is predicted to encode a 96-amino acid chimeric protein that retains all three DNA-binding domains (AT hooks) of HMGA2, but that is shorter than the original HMGA2 protein. Since the general structure of the fusion gene is similar to other previously described HMGA2 fusions, its biologic activity is predicted to be likely similar.

HMGA1 and HMGA2 rearrangements in mass-forming endometriosis

Endometriosis is a common gynecologic disorder characterized by ectopic endometrium associated with pelvic pain and infertility. The pathogenesis of endometriosis is unclear, and several genetic, endocrine, immune, and environmental agents have been studied as putative causative factors. However, consistent somatic genetic alterations have not been identified. Rarely, endometriosis presents as a mass lesion with an infiltrative pattern reminiscent of malignancy. We describe cytogenetic and molecular cytogenetic findings of mass-forming endometriosis. The index case of pulmonary endometriosis underwent conventional and molecular cytogenetics analysis. In addition, 16 cases of mass-forming endometriosis, 11 cases of usual endometriosis, and six endometriomas were investigated by fluorescence in situ hybridization (FISH) for HMGA1 and HMGA2 loci, performed on paraffin-embedded thin tissue sections with custom-designed probes. The index patient had an endometriotic lung nodule, with a 46,XX, t(5;6)(q13;p21) karyotype and HMGA1 rearrangement by FISH. A second patient had decidualized endometriosis forming a large abdominal mass and HMGA1 rearrangement by FISH. Of the 15 other cases of mass-forming endometriosis, one had HMGA1 rearrangement and two had HMGA2 rearrangement. The rearrangements were found in the stromal component exclusively. None of the usual endometriosis cases or endometriomas had HMGA1 or HMGA2 rearrangements. In conclusion, mass-forming endometriosis is an uncommon subset of endometriosis that harbors HMGA1 or HMGA2 rearrangements in up to 29% of cases. The present findings support the concept that endometriosis is clonal and that rearrangement of HMGA genes likely contributes to its pathogenesis.

Carboxypeptidase M: a biomarker for the discrimination of well-differentiated liposarcoma from lipoma

The discrimination between well-differentiated liposarcomas/atypical lipomatous tumors and lipomas can be diagnostically challenging at the histological level. However, cytogenetic identification of ring and giant rod chromosomes supports the diagnosis of well-differentiated liposarcoma/atypical lipomatous tumor. These abnormal chromosomes are mainly composed of amplified genomic sequences derived from chromosome 12q13-15, and contain several genes, including MDM2, CDK4 (SAS), TSPAN31, HMGA2, and others. MDM2 is consistently amplified in well-differentiated liposarcomas/atypical lipomatous tumors, and up to 25% in other sarcomas. As part of a large genomic study of lipomatous neoplasms, we initially found CPM to be consistently amplified in well-differentiated liposarcomas/atypical lipomatous tumors. To further explore this initial finding, we investigated the copy number status of MDM2 and CPM by fluorescent in situ hybridization (FISH) on a series of 138 tumors and 17 normal tissues, including 32 well-differentiated liposarcoma/atypical lipomatous tumors, 63 lipomas, 11 pleomorphic lipomas, 2 lipoblastomas, 30 other tumors and 17 normal fat samples. All 32 well-differentiated liposarcoma/atypical lipomatous tumors showed amplification of MDM2 and CPM, usually >20 copies per cell. The other tumors lacked MDM2 and/or CPM amplification. Chromogenic in situ hybridization confirmed the above results on a subset of these tumors (n=27). These findings suggest that identification of CPM amplification could be used as an alternative diagnostic tool for the diagnosis of well-differentiated liposarcoma/atypical lipomatous tumors.

Pseudosarcomatous fibroblastic/myofibroblastic proliferation in perinephric adipose tissue adjacent to renal cell carcinoma: a lesion mimicking well-differentiated liposarcoma

Cytologically atypical stromal cells were found in the perinephric adipose tissue, mimicking well-differentiated liposarcoma in 12 of 59 (20%) consecutive nephrectomy specimens that were resected for renal cell carcinoma. Morphologically, the atypical cells included enlarged, hyperchromatic spindle cells and floret-type multinucleate cells. Of 59, 10 (17%) renal cell carcinomas invaded through the renal capsule into the perinephric adipose tissue. Of these cases, three (30%) contained the aforementioned atypical cells. In contrast, 9 of 49 cases without extrarenal invasion (18%) contained the atypical stromal cells. Of the 12 cases with atypical stromal cells, 3 (25%) were associated with extrarenal involvement. The atypical spindle cells exhibited focal to variable positivity for smooth muscle actin and desmin in 3 of the 14 cases (including two cases from our consultation files) each. Cytokeratin AE1/AE3, cytokeratin Cam 5.2, cytokeratin 7, epithelial membrane antigen, and S-100 were negative in all cases. Amplification of MDM2 gene region, which is commonly observed in well-differentiated liposarcoma, was absent by fluorescence in situ hybridization (FISH) in the atypical stromal cells. Immunohistochemistry and FISH suggest that the atypical cells are most consistent with reactive fibroblasts/myofibroblasts. Recognition of these atypical fibroblasts/myofibroblasts may help in avoiding the potential pitfall of misdiagnosing them as well-differentiated liposarcoma.

Frequency and characterization of HMGA2 and HMGA1 rearrangements in mesenchymal tumors of the lower genital tract

Mesenchymal tumors of the lower genital tract predominantly occur in women of reproductive age and are mainly represented by aggressive angiomyxoma (AAM) and angiomyofibroblastoma (AMF). Whether these tumors are different phenotypic expressions of the same biological entity is still debatable. Genetic rearrangements of HMGA2 have been reported in a few cases of AAM but its frequency and clinicobiological implications have not been studied systematically. We evaluated 90 cases of mesenchymal tumors of the lower genital tract that comprised 42 AAMs, 18 AMFs, 6 cellular angiofibromas, 5 fibroepithelial stromal polyps, 15 genital leiomyomas, 3 superficial angiomyxomas, and 1 spindle cell lipoma. Fluorescence in situ hybridization was used to identify rearrangements of HMGA2 and its homologue HMGA1. HMGA2 rearrangements were identified in 14 AAMs (33%) and in 1 vaginal leiomyoma. All other tumors were negative for HMGA2 rearrangements. HMGA1 rearrangement was not found in any of the cases. RT-PCR confirmed transcriptional upregulation of HMGA2 only in tumors with HMGA2 rearrangements. Standard cytogenetic analyses were performed in two AAMs and one AMF. One AAM had a t(1;12)(p32;q15); the other tumors had normal karyotypes. Mapping and sequence analysis of the breakpoint showed fusion to the 3' untranslated region of HMGA2 to genomic sequences derived from the contig NT 032977.8 on chromosome 1p32. Our findings support the hypothesis that AAM and AMF are distinct biological entities. The diagnostic usefulness of HMGA2 rearrangements to differentiate between AAM and other tumors of the lower genital tract may be limited due to the their low frequency.

Formation of the 12q14-q15 Amplicon Precedes the Development of a Well-differentiated Liposarcoma Arising From a nonchondroid Pulmonary Hamartoma

Pulmonary hamartoma is a benign neoplasm that rarely recurs or undergoes malignant transformation. Herein, we report a 48-year-old woman with a history of an incomplete excised nonchondroid pulmonary hamartoma presenting as an indolent tumor recurrence. Excision of the tumor revealed a well-differentiated liposarcoma arising from the hamartomatous component. Fluorescence in situ hybridation analysis for HMGA2 and MDM2 was performed on both hamartomatous and liposarcomatous component. MDM2 and HMGA2 amplification were found in a subset of stromal cells in the hamartomatous component and in most cells of the well-differentiated liposarcoma. No rearrangement HMGA2 was found in the pulmonary hamartoma component. These findings suggest that the formation of the 12q14-q15 chromosome amplicon, the characteristic cytogenetic finding of well-differentiated liposarcomas and the structural genomic component of the supernumerary ring and giant rod chromosomes, occurred before the morphologic changes characteristic of these malignant adipose tissue tumors and likely represents a very early molecular event in their development.

A candidate tumor suppressor HtrA1 is downregulated in ovarian cancer

We report here that HtrA1, a candidate tumor suppressor, is downregulated in ovarian cancer. Expression of HtrA1 is downregulated in five of seven ovarian cancer cell lines. In total, 59% of primary ovarian tumors have either a complete absence or markedly reduced levels of HtrA1 expression compared to the brushings of ovarian surface epithelium. Primary ovarian tumors show high frequencies of loss of an allele at microsatellite markers near htrA1 locus on 10q26. Downregulation of HtrA1 in SKOV3 by antisense transfection promotes anchorage-independent growth, while exogenous expression of HtrA1 in OV202 induces cell death. HtrA1-induced cell death is not inhibited by the broad caspase inhibitor, zVAD(OMe)fmk, but instead reflects serine protease activity associated with HtrA1. These observations raise the possibility of HtrA1 as a candidate tumor suppressor involved in promoting serine-protease-mediated cell death and that downregulation of HtrA1 in ovarian cancer may contribute to malignant phenotype.