Characterization of a Molecularly Distinct Subset of Oncocytic Pleomorphic Adenomas/Myoepitheliomas Harboring Recurrent ZBTB47-AS1::PLAG1 Gene Fusion

Recurrent gene fusions are common in salivary gland tumors including benign tumors, such as pleomorphic adenoma (PA) and myoepithelioma (ME). In cases where chromosomal rearrangement is identified in the pleomorphic adenoma gene 1 (PLAG1) gene, different gene partners are found. Oncocytic metaplasia, characterized by oncocytes with abundant eosinophilic granular cytoplasm and hyperchromatic nuclei, is a well-known phenomenon in salivary gland neoplasms. However, the pure oncocytic variant of PA/ME showed PLAG1 gene rearrangements involving various gene partners at the molecular level, without any recurrent fusion being found. Our study includes 20 cases of PA/ME, with 11 females and 9 males. The age of patients ranged from 37 to 96 years, with a median age of 62.8 years. Most tumors originate from the parotid gland. The median size of the tumor was 26.5 mm (range: 13 to 60 mm). Among the 20 cases, 14 were a pure oncocytic variant of PA/ME, whereas 6 cases showed focal oncocytic or oncocytic-like aspects. Molecular studies on 20 cases of PA/ME were conducted. A novel recurrent ZBTB47-AS1::PLAG1 fusion was identified in 6 of 12 cases with pure oncocytic metaplasia, whereas the other cases had PLAG1 gene fusion with different gene partners. The transcriptomic analysis of the cases harboring ZBTB47-AS1::PLAG1 fusion demonstrated that these tumors have a distinct molecular profile from conventional PA/ME. This study reveals a unique subset in the oncocytic PA/ME spectrum characterized by pure oncocytic morphology with larger oncocytic cells and recurrent ZBTB47-AS1::PLAG1 fusion. It also highlights the transcriptomic distinctness of salivary gland adenomas with pure oncocytic metaplasia in the spectrum of salivary gland neoplasms. Further studies are needed to better understand the oncocytic variant of PA/ME and to determine the true nature of oncocytic cells in PA/ME.

SOX10-Internal Tandem Duplications and PLAG1 or HMGA2 Fusions Segregate Eccrine-Type and Apocrine-Type Cutaneous Mixed Tumors

Cutaneous mixed tumors exhibit a wide morphologic diversity and are currently classified into apocrine and eccrine types based on their morphologic differentiation. Some cases of apocrine-type cutaneous mixed tumors (ACMT), namely, hyaline cell-rich apocrine cutaneous mixed tumors (HCR-ACMT) show a prominent or exclusive plasmacytoid myoepithelial component. Although recurrent fusions of PLAG1 have been observed in ACMT, the oncogenic driver of eccrine-type cutaneous mixed tumors (ECMT) is still unknown. The aim of the study was to provide a comprehensive morphologic, immunohistochemical, and molecular characterization of these tumors. Forty-one cases were included in this study: 28 cases of ACMT/HCR-ACMT and 13 cases of ECMT. After morphologic and immunohistochemical characterization, all specimens were analyzed by RNA sequencing. By immunohistochemistry, all cases showed expression of SOX10, but only ACMT/HCR-ACMT showed expression of PLAG1 and HMGA2. RNA sequencing confirmed the presence of recurrent fusion of PLAG1 or HMGA2 in all cases of ACMT/HCR-ACMT, with a perfect correlation with PLAG1/HMGA2 immunohistochemical status, and revealed internal tandem duplications of SOX10 (SOX10-ITD) in all cases of ECMT. Although TRPS1::PLAG1 was the most frequent fusion, HMGA2::WIF1 and HMGA2::NFIB were detected in ACMT cases. Clustering analysis based on gene expression profiling of 110 tumors, including numerous histotypes, showed that ECMT formed a distinct group compared with all other tumors. ACMT, HCR-ACMT, and salivary gland pleomorphic adenoma clustered together, whereas myoepithelioma with fusions of EWSR1, FUS, PBX1, PBX3, POU5F1, and KLF17 formed another cluster. Follow-up showed no evidence of disease in 23 cases across all 3 tumor types. In conclusion, our study demonstrated for the first time SOX10-ITD in ECMT and HMGA2 fusions in ACMT and further refined the prevalence of PLAG1 fusions in ACMT. Clustering analyses revealed the transcriptomic distance between these different tumors, especially in the heterogenous group of myoepitheliomas.

An intraosseous myoepithelial carcinoma with a EWSR1::PBX3 fusion

Herein we report a case of an intraosseous myoepithelial carcinoma harboring a EWSR1::PBX3 fusion gene. The patient was a 64-year-old male found to have a 7 cm destructive lesion in the distal ulna with an extraosseous soft tissue component. Microscopic examination of the resected tumor showed a spindle-cell lesion within a sclerotic stroma and intravascular tumor emboli. At higher power the tumor cells showed moderate nuclear atypia with a high mitotic count (20 per mm2 ). Immunohistochemistry revealed diffuse EMA positivity and focal pancytokeratin (AE1/AE3) and S100 expression, consistent with myoepithelial differentiation. NGS using the Oncomine Childhood Cancer Assay (Thermo Fisher Scientific, Inc.) revealed a EWSR1-PBX3 fusion and ABL amplification. The patient subsequently developed local recurrence as well as distant lymph node, lung and vertebral metastases; he is currently awaiting systemic treatment in the context of a clinical trial. In this report, we present a rare case of a skeletal myoepithelial tumor harboring a EWSR1::PBX3 fusion with demonstrated histological and clinical features of malignancy.

NKX3.1 Expression and Molecular Characterization of Secretory Myoepithelial Carcinoma (SMCA): Advancing the Case for a Salivary Mucous Acinar Phenotype

BACKGROUND

Secretory myoepithelial carcinomas (SMCA) are rare, mucinous, signet ring predominant tumors with primitive myoepithelial features. While many mucinous salivary gland tumors have now been molecularly characterized, key drivers in SMCA have yet to be elucidated. Recently, NKX3.1, a homeodomain transcription factor implicated in salivary mucous acinar development was also shown in a subset of salivary mucinous neoplasms, salivary intraductal papillary mucinous neoplasms (SG-IPMN). To date, NKX3.1 expression has not been characterized in other mucinous salivary lesions. Here, we report molecular and extended immunophenotypic findings in SMCA and NKX3.1 expression in the context of other head and neck lesions.

METHODS

We retrieved 4 previously reported SMCA, performed additional immunohistochemical and targeted next-generation sequencing (NGS). We also investigated the use of NKX3.1 as a marker for SMCA in the context of its prevalence and extent (using H-score) in a mixed cohort of retrospectively and prospectively tested head and neck lesions (n = 223) and non-neoplastic tissues (n = 66).

RESULTS

NKX3.1 positivity was confirmed in normal mucous acini as well as in mucous acinar class of lesions (5/6, mean H-score: 136.7), including mucinous adenocarcinomas (3/4), SG-IPMN (1/1), and microsecretory adenocarcinoma (MSA) (1/1). All SMCA were positive. Fluorescence in situ hybridization for SS18 rearrangements were negative in all successfully tested cases (0/3). NGS was successful in two cases (cases 3 and 4). Case 3 demonstrated a PTEN c.655C>T p.Q219* mutation and a SEC16A::NOTCH1 fusion while case 4 (clinically aggressive) showed a PTEN c.1026+1G>A p.K342 splice site variant, aTP53 c.524G>A p.R175H mutation and a higher tumor mutation burden (29 per Mb). PTEN immunohistochemical loss was confirmed in both cases and a subset of tumor cells showed strong (extreme) staining for P53 in Case 4.

CONCLUSION

Despite a partial myoepithelial phenotype, SMCA, along with mucinous adenocarcinomas/SG-IPMN and MSA, provisionally constitute a mucous acinar class of tumors based on morphology and NKX3.1 expression. Like salivary mucinous adenocarcinomas/SG-IPMN, SMCA also show alterations of the PTEN/PI3K/AKT pathway and may show progressive molecular alterations. We document the first extramammary tumor with a SEC16A::NOTCH1 fusion.

The Diagnostic Utility of RAS Q61R Mutation-specific Immunohistochemistry in Epithelial-Myoepithelial Carcinoma

Epithelial-myoepithelial carcinoma (EMC) is a rare salivary gland cancer characterized by biphasic tubular structures composed of inner ductal and outer clear myoepithelial cells. Because of its histologic variety and overlap of histologic features with other salivary gland tumors, there are broad differential diagnoses. The HRAS Q61R mutation has been reported to be frequent in and specific to EMC. We evaluated the usefulness of RAS Q61R mutant-specific immunohistochemical (IHC) staining for detecting this genetic alteration in EMC. We investigated 83 EMC cases and 66 cases of salivary gland tumors with an EMC-like component, including pleomorphic adenoma, adenoid cystic carcinoma, basal cell adenoma/adenocarcinoma, and myoepithelial carcinoma. Sanger sequencing was performed for HRAS, KRAS, and NRAS. The diffuse and membranous/cytoplasmic RAS Q61R IHC expression was observed in 65% of EMC cases, in which all cases harbored the HRAS Q61R mutation. IHC-positive cases were present only in de novo EMCs (54/76 cases, 71%) but not in EMCs ex pleomorphic adenoma. The immunoreactivity was almost always restricted to the myoepithelial cells. Conversely, all EMC cases lacking the HRAS Q61R mutation were negative on IHC. In addition, only 3% of EMC-like tumors showed the abovementioned immunopositivity. None of the cases examined carried KRAS or NRAS mutations. IHC for RAS Q61R is highly sensitive and specific for detecting the HRAS Q61R mutation in EMC. Since significant immunopositivity was almost exclusively identified in nearly two thirds of EMCs but seldom in the histologic mimics, the IHC of RAS Q61R is a useful tool for diagnosing EMC in general pathology laboratories.

Molecular Profiling of Clear Cell Myoepithelial Carcinoma of Salivary Glands With EWSR1 Rearrangement Identifies Frequent PLAG1 Gene Fusions But No EWSR1 Fusion Transcripts

Myoepithelial carcinoma of salivary glands is an underrecognized and challenging entity with a broad morphologic spectrum, including an EWSR1-rearranged clear cell variant. Myoepithelial carcinoma is generally aggressive with largely unknown genetic features. A retrospective review of Salivary Gland Tumor Registry in Pilsen searching for the key words "clear cell myoepithelial carcinoma," "hyalinizing clear cell," and "clear cell malignant myoepithelioma" yielded 94 clear cell myoepithelial carcinomas (CCMCs) for molecular analysis of EWSR1 rearrangement using fluorescence in situ hybridization (FISH). Tumors positive for EWSR1 gene rearrangement were tested by next-generation sequencing (NGS) using fusion-detecting panels. NGS results were confirmed by reverse-transcription polymerase chain reaction or by FISH. Twenty-six tumors originally diagnosed as CCMC (26/94, 27.6%) revealed split signals for EWSR1 by FISH. Six of these tumors (6/26, 23%) displayed amplification of the EWSR1 locus. Fifteen cases were analyzable by NGS, whereas 9 were not, and tissue was not available in 2 cases. None of the CCMCs with EWSR1 rearrangements detected by FISH had an EWSR1 fusion transcript. Fusion transcripts were detected in 6 cases (6/15, 40%), including LIFR-PLAG1 and CTNNB1-PLAG1, in 2 cases each, and CHCHD7-PLAG1 and EWSR1-ATF1 fusions were identified in 1 case each. Seven cases, including those with PLAG1 fusion, were positive for PLAG1 rearrangement by FISH, with notable exception of CHCHD7-PLAG1, which is an inversion not detectable by FISH. One single case with EWSR1-ATF1 fusion in NGS showed ATF1 gene rearrangement by FISH and was reclassified as clear cell carcinoma (CCC). In addition, another 4 cases revealed ATF1 rearrangement by FISH and were reclassified as CCC as well. Moreover, 12/68 (17%) CCMCs with intact EWSR1 gene were selected randomly and analyzed by NGS. PLAG1 fusions were found in 5 cases (5/12, 41.6%) with LIFR (2 cases), FGFR1 (2 cases), and CTNNB1 (1 case) as partner genes. Overall, PLAG1 gene rearrangements were detected in 10/38 (26%) tested cases. None of the tumors had SMARCB1 loss by immunohistochemistry as a possible explanation for the EWSR1 abnormalities in FISH. Novel findings in our NGS study suggest that EWSR1-FISH positive CCMC is a gene fusion-driven disease with frequent oncogenic PLAG1 fusions, including LIFR-PLAG1 and CTNNB1-PLAG1 in most cases. Productive EWSR1 fusions are found only in a minority of EWSR1-ATF1-rearranged cases, which were in part reclassifiable as CCCs. Detectable EWSR1-FISH abnormality in CCMCs without gene fusion perhaps represents a passenger mutation with minor or no oncologic effect.

Ex vivo assessment of targeted therapies in a rare metastatic epithelial-myoepithelial carcinoma

Epithelial-myoepithelial carcinoma (EMC) is a rare subtype of salivary gland neoplasms. Since the initial description of the cancer, just over 300 cases have been reported. EMCs occupy a biphasic cellular differentiation-state defined by the constitution of two cell types representing epithelial and myoepithelial lineages, yet the functional consequence of the differentiation-state heterogeneity with respect to therapy resistance of the tumors remains unclear. The reported local recurrence rate of the cases is approximately 30%, and while distant metastases are rare, a significant fraction of these cases are reported to receive no survival benefit from radio- or chemotherapy given in addition to surgery. Moreover, no targeted therapies have been reported for these neoplasms. We report here the first use and application of ex vivo drug screening together with next generation sequencing to assess targeted treatment strategies for a rare metastatic epithelial-myoepithelial carcinoma. Results of the ex vivo drug screen demonstrate significant differential therapeutic sensitivity between the epithelial and myoepithelial intra-tumor cell lineages suggesting that differentiation-state heterogeneity within epithelial-myoepithelial carcinomas may present an outlet to partial therapeutic responses to targeted therapies including MEK and mTOR inhibitors. These results suggest that the intra-tumor lineage composition of EMC could be an important factor to be assessed when novel treatments are being evaluated for management of metastatic EMC.

Primary cutaneous biphasic sarcomatoid basal cell carcinoma with myoepithelial carcinoma differentiation: A new variant

Isolated cases of basal cell carcinoma (BCC) with partial myoepithelial component have been described. However, myoepithelial differentiation has not been described in sarcomatoid basal cell carcinomas, which usually show features resembling osteosarcoma, chondrosarcoma, or leiomyosarcoma. We report a case of an 87-year-old man with a forehead lesion that histologically showed a minor component of conventional nodular BCC in transition with a major biphasic sarcomatoid growth composed of invasive spindle-cell and epithelial-like components, the latter with a reticular pattern and scattered ductal structures. Both components showed cytological atypia and high mitotic rate (26/10HPF), with atypical mitotic figures. BER-EP4 immunostaining was exclusively found in the nodular BCC component whereas the sarcomatoid component revealed immunostaining for α-smooth muscle actin (SMA), muscle-specific actin (MSA), calponin, and p63 in both epithelial-like and spindle-cell populations. Focal immunoreactivity was observed in the epithelial component for S100 and glial fibrillary acidic protein (GFAP). Furthermore, EWSR1-PBX1 gene fusion was also detected. This is to our knowledge, the first fully documented case of biphasic sarcomatoid BCC with myoepithelial carcinoma differentiation.

A first case report of primary epithelial myoepithelial carcinoma-like renal tumor showing a perivascular pseudorosette-like pattern: Description of morphologic, immunohistochemical, and genetic features

RATIONALE

Over the past decade, although several new entities of renal tumors have emerged, a form of renal cell carcinoma (RCC) that morphologically resembles epithelial-myoepithelial carcinoma has not been reported thus far. Herein, we describe a case of an unusual renal tumor that remained unclassified under a current RCC subtype, and briefly present its morphologic, immunophenotypic, and genetic features.

PATIENT CONCERNS

The patient was an 85-year-old man who presented with hematuria and flank pain. Imaging studies revealed a left renal mass without enlarged lymph nodes. There were no abnormal masses or nodules in other organs.

DIAGNOSES

The patient underwent no other treatment except the left radical nephrectomy under a clinical diagnosis of invasive urothelial carcinoma and was discharged on the thirteenth day. Histologically, the renal tumor showed biphasic proliferation of epithelial (strongly cytokeratin-positive; P63, P40, and vimentin-negative) and myoepithelial (strongly vimentin-positive; focal P63 and P40-positive; and weakly cytokeratin-positive) cells arranged in a perivascular pseudorosette-like pattern. No mutations were detected in multiple gene tests. According to the pathological structure, the patient was diagnosed as primary epithelial myoepithelial carcinoma-like renal tumor.

INTERVENTIONS

To the best of our knowledge, the present tumor has not been previously described, and thus, this variant has not been integrated into a known form of PCC. Therefore, we cannot diagnose this type of tumor with other types of kidney tumors.

OUTCOMES

Three years after primary diagnosis, the patient died of multiple organ failure result from multiple distant metastases.

LESSONS

We present the first case of carcinoma of the kidney with EMC-like features and a perivascular pseudorosette-like growth pattern. Clinicians should be aware of the features of this uncommon variant of RCC to avoid diagnostic delays or misdiagnosis and prevent unnecessary or inappropriate treatment.

Myoepithelial Tumors of Bone

Myoepithelial tumors (METs) of bone (BMETs) are a rare but distinct tumor entity. METs that are cytologically benign are termed myoepitheliomas; METs with malignant histologic features are called myoepithelial carcinomas. BMETs have a wide age range, may involve any part of the skeleton, and have a variable spindle cell and epithelioid morphology. Bone tumors to be considered in the differential diagnosis are discussed. Additional techniques are indispensable to correctly diagnose BMETs. By immunohistochemistry, BMETs often express cytokeratins and/or EMA together with S100, GFAP, or calponin. Half of BMETs harbor EWSR1 (or rare FUS) gene rearrangements with different gene partners.

Myoepithelial carcinoma of the stomach: A diagnostic pitfall

Myoepithelioma/myoepithelial carcinomas are not commonly found in soft tissues and are especially rare at visceral sites. This report describes a case of a rare low-grade myoepithelial carcinoma of the stomach. A 61-year-old female patient presented with postprandial abdominal discomfort. Endoscopy revealed a 1.1 cm submucosal lesion. Local excision was performed after malignancy was confirmed by biopsy. The resection margin is free of tumor and she received no adjuvant therapy. The tumor was characterized by multinodular growth with biphasic epithelioid and spindle components. Infiltrative margin and nuclear pleomorphism are seen. Tumor cells were positive for both epithelial and myoepithelial markers. Evidence of epithelial differentiation was confirmed by electron microscopy. No EWSR1 rearrangement was detected. The final diagnosis was low-grade myoepithelial gastric carcinoma. The patient is currently well, and no evidence of recurrence or metastasis was found after ten-month of follow-up. Myoepithelial carcinoma should be considered in the differential diagnosis of a biphasic gastric tumor.

Novel FUS-KLF17 and EWSR1-KLF17 fusions in myoepithelial tumors

Myoepithelial (ME) tumors of soft tissue and bone display a heterogeneous histologic spectrum and in about half of the cases harbor EWSR1 gene rearrangements. Despite rare case reports, the prevalence of fused in sarcoma (FUS) gene abnormalities and its related fusion partners remains undetermined among ME tumors. Therefore, we screened 66 EWSR1-negative ME tumors for FUS abnormalities by fluorescence in situ hybridization (FISH). In an index FUS-rearranged case, 3'-rapid amplification of cDNA ends (RACE) was applied to identify the fusion partner. Results were further confirmed by reverse transcription-PCR, followed by FISH screening the entire cohort of FUS-rearranged and EWSR1-positive ME lesions lacking a known fusion partner. The correlation between genotype and clinicopathological features was also investigated. As a result, six (9%) FUS-rearranged cases were identified, spanning divergent age groups, tumor locations, and morphologic features. A novel FUS-KLF17 fusion was identified by 3'-RACE in an 11-year-old girl with a foot lesion associated with locoregional metastases. Three additional cases with FUS-KLF17 fusions were identified and one KLF17 rearrangement (6.3%) was found among the 16 EWSR1-positive cases tested. The KLF17-related ME tumors affected younger patients and often exhibited trabecular growth in a myxohyaline stroma, but this genotype did not correlate with a malignant phenotype. In conclusion, a small subset of ME tumors harbor FUS rearrangements, two thirds of them being associated with KLF17 fusion. FUS FISH analysis is recommended in EWSR1-negative lesions in which a ME diagnosis is suspected. KLF17 is also a rare gene fusion partner to EWSR1-rearranged ME tumors.

Consistent PLAG1 and HMGA2 abnormalities distinguish carcinoma ex-pleomorphic adenoma from its de novo counterparts

Carcinoma ex-pleomorphic adenoma (CA ex-PA) is a malignant salivary gland tumor that arises in association with pleomorphic adenoma (PA). Both PA and CA ex-PA have a broad spectrum of histology, and distinction from their histologic mimics may be difficult based on morphology alone. PLAG1 and HMGA2 abnormalities are the most common genetic events in both PA and CA ex-PA; however, the use of PLAG1 and HMGA2 as adjunct molecular tests has not been well established. Fluorescence in situ hybridization for PLAG1 and HMGA2 was performed on 22 CA ex-PA (10 myoepithelial carcinomas [MECAs], 10 salivary duct carcinomas [SDCs], 1 carcinoma with squamoglandular features, and 1 mixed MECA-adenocarcinoma not otherwise specified), 20 de novo carcinomas (11 MECAs and 9 SDCs), 16 PAs, and 11 PA-histologic mimics. All except 3 CAs ex-PA (86%) were positive for PLAG1 or HMGA2 rearrangements/amplifications. In contrast, 18 (90%) of 20 de novo carcinomas lacked abnormalities in PLAG1 or HMGA2 (P < .01). PLAG1 or HMGA2 rearrangements were identified in 6 (67%) of 9 hypocellular myxoid PAs and in 2 (29%) of 7 cellular PAs. Furthermore, all morphologic mimics of PA were negative for PLAG1 or HMGA2. PLAG1 and HMGA2 rearrangements are the most common genetic events in CA ex-PA regardless of the histologic subtype. Unlike CA ex-PA, de novo carcinomas were negative for PLAG1 and HMGA2. Interestingly, rearrangements of PLAG1/HMGA2 were identified in most hypocellular PAs but only in a small subset of cellular PAs. Fluorescence in situ hybridization for PLAG1 or HMGA2 can be used to distinguish between PA and CA ex-PA and their morphologic mimics.

EWSR1-PBX3: a novel gene fusion in myoepithelial tumors

The genetics of myoepithelial tumors (ME) of soft tissue and bone have recently been investigated, with EWSR1-related gene fusions being seen in approximately half of the tumors. The fusion partners of EWSR1 so far described include POU5F1, PBX1, ZNF444 and, in a rare case, ATF1. We investigated by RNA sequencing an index case of EWSR1-rearranged ME of the tibia, lacking a known fusion partner, and identified a novel EWSR1-PBX3 fusion. The fusion was further validated by reverse transcriptase polymerase chain reaction and fluorescence in situ hybridization (FISH). To evaluate if this is a recurrent event, an additional cohort of 22 EWSR1-rearranged ME cases lacking a fusion partner were screened by FISH for abnormalities in PBX3 gene. Thus, two additional cases were identified showing an EWSR1-PBX3 gene fusion. One of them was also intraosseous involving the ankle, while the other occurred in the soft tissue of the index finger. The morphology of the EWSR1-PBX3 fusion positive cases showed similar findings, with nests or sheets of epithelioid to spindle cells in a partially myxoid to collagenous matrix. All three cases showed expression of S100 and EMA by immunohistochemistry. In summary, we report a novel EWSR1-PBX3 gene fusion in a small subset of ME, thereby expanding the spectrum of EWSR1-related gene fusions seen in these tumors. This gene fusion seems to occur preferentially in skeletal ME, with two of the three study cases occurring in intraosseous locations.

Rhabdoid Variant of Myoepithelial Carcinoma, with EWSR1 Rearrangement: Expanding the Spectrum of EWSR1-Rearranged Myoepithelial Tumors

Myoepithelial and mixed tumors represent a heterogeneous group of neoplasms for which classification is incomplete and continues to evolve. Those arising in the soft tissues appear to represent subgroups that are genetically distinct from those that occur within salivary glands. We describe a case of soft tissue myoepithelial carcinoma with rhabdoid morphology, which presented as an enlarging neck mass in a 40 year old male, and in which EWSR1 rearrangement was demonstrated by fluorescence in situ hybridization. This neoplasm showed diffuse INI1 loss, making distinction from other INI1-negative rhabdoid tumors difficult. This expands the range of reported histologic features of EWSR1-rearranged myoepithelial neoplasms, and highlights the significant morphologic and immunohistochemical overlap between this and other INI1-negative malignant rhabdoid neoplasms.

Chromosomal rearrangements in PLAG1 of myoepithelial salivary gland tumours

PLAG1 mutations are related to the development of pleomorphic adenomas. A specific aspect of PA is the histological diversity of this entity, containing cells with mesenchymal, epithelial and myoepithelial differentiation. Evidence for myoepithelial cells in PA raises the question whether the very rare entity of pure myoepithelial salivary gland tumours shows chromosomal translocations and rearrangements and whether activation of PLAG1 can be detected.

MATERIALS AND METHODS

Fluorescence in-situ hybridisation (FISH) was established using the DNA-probes PLAG 233, PLAG 234, PLAG 235. The probes were generated from plasmids. Standardization of FISH was achieved in human lymphocytes. Routinely formalin-fixed, paraffin-embedded slices of myoepithelial salivary gland tumours were available for study. In some cases isolated nuclei were investigated. Isolation of the nuclei was performed according to Hedley. Scoring of the FISH was done with a Laser-scanning microscope (spot-counting: fluorescence signals/100 cells/slice). The number of signal variants was determined. All evaluated regions were registered on microphotographs.

RESULTS

PLAG1 was only rarely detected. PLAG1 is evidently not involved in the development of myoepithelial tumours. The proportion of 8q12-alterations in myoepithelial tumours was very low.

CONCLUSION

PLAG1 is an insufficient marker to differentiate between benign and malignant myoepithelial tumours.

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.

Soft tissue high grade myoepithelial carcinoma with round cell morphology: report of a newly described entity with EWSR1 gene rearrangement

The case of soft tissue malignant myoepithelioma is presented including clinicopathological, immunohistochemical and cytogenetic findings. A 36-year-old Saudi male patient suffered from large mass involving right scapula and right shoulder joint measuring 14x13x11 mm. Core biopsy revealed sheets and lobules of poorly differentiated small malignant cells with marked atypia and frequent mitosis. Initially, immunohistochemistry was reactive for vimentin, pan-cytokeratin, EMA and CD99. The case was negative for desmin, SMA, CD34, S-100 protein and GFAP. FISH analysis exhibited negativity for SS18 (18q11.2) gene rearrangement and positivity for EWSR1 (22q12) gene rearrangement and a diagnosis of Ewing/PNET was considered. Clinical behavior and therapeutic response did not match the diagnosis with re-evaluation. Wedge biopsy demonstrated aggregates of epithelioid cells besides calponin and P63 positivity. Final diagnosis of malignant myoepithelioma with EWSR1 gene rearrangement was issued; a new entity with aggressive course. Myoepithelial carcinoma of soft tissue exhibits a wide spectrum of cytomorphology with overlapping phenotype similar to other soft tissue sarcoma like synovial sarcoma, mesenchymal chondrosarcoma, epithelioid sarcoma as well as Ewing/PNET. Moreover, a new finding of EWSR1 gene rearrangement is recognized in malignant myoepithelioma with different fusion partners. Hence, myoepithelial carcinoma should be kept in mind in diagnosis of soft tissue tumors even with unusual phenotype and gene rearrangement.

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.

The urokinase-system in tumor tissue stroma of the breast and breast cancer cell invasion

The urokinase-system has been implicated in tumor spread. The serine protease urokinase-type plasminogen activator (uPA), its receptor (uPAR) and its inhibitor (PAI-1) are involved in the control of extracellular turnover, cell migration, invasion, cell signalling, proliferation, apoptosis and angiogenesis leading to a variety of different responses, under both physiological and pathological conditions. uPA and PAI-1 were the first novel tumor biological factors to be validated at the highest level of evidence regarding their clinical utility in breast cancer. However, it is unclear whether it is their (relative) levels in the tumor stroma or in the tumor cells themselves that is the most relevant to patients outcome. This is the first study in which tumor cells and stromal tissue of invasive breast carcinomas were separated by laser capture microdissection followed by ELISA-based determination of the uPA, uPAR and PAI-1 levels. In addition, we localized uPA, uPAR and PAI-1 distribution in invasive breast cancer (n=30) and in ductal carcinoma in situ (DCIS, n=30) by immunohistochemistry and in situ hybridization. We have demonstrated that no significant differences between uPA, uPAR and PAI-1 levels in tumor stroma only, tumor cells only and not separated breast cancer tissue exist (p>0.05). Our results suggest that similar expression levels of these factors in both compartments and in not separated breast cancer tissue may have the same impact on the clinical behavior of breast cancer. These results are an important issue for practical use of tissue sampling. For using uPA and PAI-1 levels as prognostic and predictive factors in breast cancer the quantity of tumor stroma in the tumor tissue specimen is not relevant for assessment patients outcome. Our results were confirmed by immunohistochemistry and in situ hybridization analysis showing that in nearly all cases of invasive carcinomas and DCIS fibroblasts as well as macrophages strongly express uPA, uPAR and PAI-1. Prompted by our immunohistological results that nearly all myoepithelial cells of DCIS exhibit uPA, uPAR and PAI-1, we investigated these important host cells in detail. We have demonstrated by multimodal methods that uPAR and PAI-1 protein and mRNA is expressed in most myoepithelial cells of DCIS. Additionally, we furnish evidence that uPAR expression of myoepithelial cells are important for uPAR Vitronectin-associated cell-matrix interaction, which regulates cell adhesion and detachment. We speculate that the loss of the anti-invasive myoepithelial cell layer in DCIS may be triggered by PAI-1 and could be an early sign of subsequent tumor cell invasion.

Adenomyoepitheliomatous lesions of the mammary glands in transgenic mice with targeted PLAG1 overexpression

PLAG1 proto-oncogene overexpression has been causally linked to multiple tumors, highlighting its broad tumorigenic relevance. Here, the oncogenic potential of PLAG1 in mammary gland tumorigenesis was investigated in PLAG1 transgenic mice. To target mammary glands, mice of 2 independent PLAG1 transgenic strains, PTMS1 and PTMS2, in which PLAG1 expression can be modulated by Cre-mediation, were crossed with MMTV-Cre transgenic mice, resulting in P1-MCre and P2-MCre offspring, respectively. Hundred percentage of P1-MCre female mice showed mammary gland hyperplasia, caused by adenomyoepithelial adenosis, at 8 weeks. The tumorigenic process could not be studied further in P1-MCre mice, because concomitant fast-growing salivary gland tumors required euthanasia. Sixteen percentage of P2-MCre females developed mammary gland adenomyoepitheliomas within 30-45 weeks, and none displayed concomitant salivary gland tumors. To further study mammary gland tumorigenesis in PTMS1-derived mice, intercrossing with WAP-Cre transgenic mice, resulting in P1-WAPCre mice, was performed to target PLAG1 expression more specifically to mammary glands. Eighty percentage of such mice developed adenomyoepitheliomas within 53-88 weeks. All PLAG1-induced adenomyoepitheliomas revealed expression upregulation of Igf2/H19, Dlk1/Gtl2, Igfbps and Wnt signaling genes (Wnt6, Cyclin D1). Collectively, these results establish the oncogenic potential of PLAG1 in mammary glands of mice and point towards contributing roles of Igf and Wnt signaling.

Detection of a t(1;22)(q23;q12) translocation leading to an EWSR1-PBX1 fusion gene in a myoepithelioma

Chromosome banding as well as molecular cytogenetic methods are of great help in the diagnosis of mesenchymal tumors. Myoepithelial neoplasms of soft tissue including myoepitheliomas, mixed tumors, and parachordomas are diagnoses that have been increasingly recognized the last few years. It is still debated which neoplasms should be included in these morphologically heterogeneous entities, and the boundaries between them are not clear-cut. The pathogenetic mechanisms behind myoepithelial tumors are unknown. Only five parachordomas and one mixed tumor have previously been karyotyped, and nothing is known about their molecular genetic characteristics. We present a mesenchymal tumor classified as a myoepithelioma that had a balanced translocation t(1;22)(q23;q12) as the sole karyotypic change. A novel EWSR1-PBX1 fusion gene consisting of exons 1-8 of the 5'-end of EWSR1 and exons 5-9 of the 3'-end of PBX1 was shown to result from the translocation. Both genes are known to be targeted also by other neoplasia-specific translocations, PBX1 in acute lymphoblastic leukemia and EWSR1 in several solid tumors, most of which are malignant. Based on the structure of the novel fusion gene detected, its transforming mechanism is thought to be the same as for other fusion genes involving EWSR1 or PBX1.

WIF1, an inhibitor of the Wnt pathway, is rearranged in salivary gland tumors

Chromosome rearrangements involving 12q13-15 are frequent among several tumors, including pleomorphic adenomas. The common molecular target for these aberrations is the HMGA2 gene, but various fusion partners of HMGA2 have been reported in tumors. Here we report the identification of the WNT inhibitory factor 1 (WIF1) gene as a novel HMGA2 fusion partner in a salivary gland pleomorphic adenoma. In normal salivary gland tissue WIF1 is expressed at a high level and HMGA2 is not expressed. However, in the pleomorphic adenoma expressing the HMGA2/WIF1 fusion transcript, we observed re-expression of HMGA2 wild-type transcripts and very low levels of WIF1 expression. These data suggest a possible synergistic effect between upregulation of HMGA2 and downregulation of WIF1. We screened 13 additional benign and malignant salivary gland tumors and detected WIF1 rearrangement in one out of two carcinomas ex-pleomorphic adenoma analyzed. In this malignant tumor, the rearrangement of one WIF1 allele coexists with loss of the other allele, a classic signature of a tumor suppressor gene. WIF1 is an antagonist of the Wnt signaling pathway, which plays a critical role in human cancer. In transgenic mouse models, Wnt activation leads to a high frequency of benign and malignant salivary gland tumors. To our knowledge, this is the first report suggesting that WIF1 is a recurrent target in human salivary gland oncogenesis and that downregulation of WIF1 plays a role in the development and/or progression of pleomorphic adenomas.

Myoepithelial carcinoma arising in an adenomyoepithelioma of the breast: Case report with immunohistochemical and mutational analysis

Adenomyoepithelioma (AME) of the breast is an uncommon tumor characterized by biphasic proliferation of both epithelial and myoepithelial cells. In rare instances, the epithelial, the myoepithelial or both components of an AME may become malignant. Described herein is the case of a 69-year-old woman who presented with myoepithelial carcinoma of the breast in an AME. Malignancy of myoepithelial component (MEC) was evidenced by the presence of cytological atypia, high mitotic rate, necrosis and local invasion. Immunohistochemical study demonstrated strong expression of P53 and phosphorylated extracellular signal-regulated kinase 1/2 in MEC. Laser capture microdissection technique and mutational analysis further revealed point mutation of the p53 gene (T-->G transversion at codon 270) in this population, but not in glandular epithelial cells or adjacent normal ductal epithelium. No mutations in exons 1 and 2 of the K-, H-, and N-ras genes were identified in any of the neoplastic component. To the authors' knowledge this is the first report of a mutation in the p53 gene in a malignant AME of the breast.

[Immunohistochemical characterization of salivary gland tumors with tissue micro-arrays]

Systematic analysis of gene expression in salivary gland tumors is necessary to identify genes associated with specific tumor types. From the salivary gland register of the University Hospital Hamburg-Eppendorf sufficient samples of various tumors were available to generate Tissue Micro-Arrays (TMA). In light of the considerable heterogeneity of salivary gland tumors, this study was aimed at evaluating the suitability of TMA in salivary gland diagnostics and research. Epithelial antigens are not sufficient for a tumor-type-specific characterization. Myoepithelial markers are suitable for distinguishing biphasic tumor types from purely epithelial tumors. The detection of amylase in acinic cell carcinomas, and the detection of steroid hormone receptors in these and other malignant salivary gland tumors particularly in combination with the expression of transcription factors, oncogenes and proliferation associated antigens result in characteristic expression profiles. These may prove to be valuable for further investigations, especially on the molecular level.

Cytokinesis failure generating tetraploids promotes tumorigenesis in p53-null cells

A long-standing hypothesis on tumorigenesis is that cell division failure, generating genetically unstable tetraploid cells, facilitates the development of aneuploid malignancies. Here we test this idea by transiently blocking cytokinesis in p53-null (p53-/-) mouse mammary epithelial cells (MMECs), enabling the isolation of diploid and tetraploid cultures. The tetraploid cells had an increase in the frequency of whole-chromosome mis-segregation and chromosomal rearrangements. Only the tetraploid cells were transformed in vitro after exposure to a carcinogen. Furthermore, in the absence of carcinogen, only the tetraploid cells gave rise to malignant mammary epithelial cancers when transplanted subcutaneously into nude mice. These tumours all contained numerous non-reciprocal translocations and an 8-30-fold amplification of a chromosomal region containing a cluster of matrix metalloproteinase (MMP) genes. MMP overexpression is linked to mammary tumours in humans and animal models. Thus, tetraploidy enhances the frequency of chromosomal alterations and promotes tumour development in p53-/- MMECs.

Myoepitheliale Tumoren der Kopfspeicheldrüsen

This tutorial focuses on myoepithelial tumors of salivary glands, an entity with heterogeneous cytomorphology and inconsistent immunophenotype. Moreover, the clinical course cannot be predicted reliably from cytomorphological and immunophenotypic analysis. This heterogeneity causes problems in routine diagnostic, so that diagnosis ultimately rests on conventional histology. In a representative series of myoepitheliomas and malignant myoepitheliomas, antibodies against cytokeratins 5/6, S 100 protein and vimentin produced the most consistent reactivity profile. Staining for cytokeratins 5/6 is a useful addition to the established immunohistologic marker panel in the work-up of myoepitheliomas, because of its reliable expression in most cases and because it may underline the epithelial nature of the lesion. Comparative genomic hybridisation (CGH) profiles of myoepitheliomas and myoepithelial carcinomas showed no chromosomal aberration in less than 50% of myoepithelial carcinomas, so that CGH is of limited help in a given case. In a case that was represented in three separately localized manifestations of the disease that differed in their CGH profiles, gross genetic aberrations suggest to be acquired during tumor progression and should raise the suspicion of malignancy. Thus, diagnosis of myoepithelial tumors of salivary glands has to rest on morphological grounds with support of a restricted panel of immunohistologic markers.

[Myoepithelioma of soft tissue -- case report with clinicopathologic, ultrastructural, and cytogenetic findings]

The case of a soft tissue myoepithelioma is presented including clinicopathologic, ultrastructural, and genetic findings. A 30-year-old male patient suffered from a soft tissue tumor within the deep soft tissues of the right lower leg measuring 13.2 x 8.2 x 9 cm. Histologically, the lesion was diagnosed as a myoepithelioma displaying a lobulated architecture with cords and nests of epithelioid and spindle cells without cytologic atypia lying within a fibromyxoid and partly chondroid matrix; immunohistochemistry was positive for pancytokeratin, S100-protein, calponin and partly for GFAP and EMA. Ultrastructural analysis revealed glycogen deposits and cell-membrane-associated plaque structures, whereas true myofilaments could not be identified (with immunohistochemistry being negative for actin). Using comparative genomic hybridization (CGH), a gain of chromosome Y was detected. A loss on 17p could not be detected unambiguously. However, based on the low resolution of CGH a small loss cannot be excluded. The patient was free of disease 25 months following complete tumor resection. Myoepitheliomas/mixed tumors of deep soft tissue represent rare soft tissue lesions that may reach a considerable size and may mimic other soft tissue tumors or sarcomas. Based on a local relapse rate of approximately 20% according to the literature, a complete resection with thorough follow-up should be recommended.

Gene expression profile of an adenomyoepithelioma of the breast with a reciprocal translocation involving chromosomes 8 and 16

Myoepithelium is an integral part of the mammary ductal and lobular architecture, positioned between luminal cells and the basement membrane. We describe the first report on cytogenetic findings in an adenomyoepithelioma of the breast with a balanced t(8;16)(p23;q21), and provide gene expression profile using Affymetrix GeneChip U95AV2 (Affymetrix, Santa Clara, CA). Differential analysis identified 857 genes with 2-fold or more mRNA change in comparison to pooled normal breast control; immunohistochemical analysis was used to confirm these results in a limited number of genes. Expression results were grouped based on the chromosomal location of the genes and associated protein function, and identified several potential pathogenetic mechanisms (autocrine and paracrine growth stimuli) in the development of myoepithelial tumors.

Expression of ATM, p53, and the MRE11-Rad50-NBS1 complex in myoepithelial cells from benign and malignant proliferations of the breast

AIMS

To analyse the expression of proteins involved in DNA double strand break detection and repair in the luminal and myoepithelial compartments of benign breast lesions and malignant breast tumours with myoepithelial differentiation.

METHODS

Expression of the ataxia telangiectasia (ATM) and p53 proteins was immunohistochemically evaluated in 18 benign and malignant myoepithelial tumours of the breast. Fifteen benign breast lesions with prominent myoepithelial compartment were also evaluated for these proteins, in addition to those in the MRE11-Rad50-NBS1 (MRN) complex, and the expression profiles were compared with those seen in eight independent non-cancer (normal breast) samples and in the surrounding normal tissues of the benign and malignant tumours examined.

RESULTS

ATM expression was higher in the myoepithelial compartment of three of 15 benign breast lesions and lower in the luminal compartment of eight of these lesions compared with that found in the corresponding normal tissue compartments. Malignant myoepithelial tumours overexpressed ATM in one of 18 cases. p53 was consistently negative in benign lesions and was overexpressed in eight of 18 malignant tumours. In benign breast lesions, expression of the MRN complex was significantly more reduced in myoepithelial cells (up to 73%) than in luminal cells (up to 40%) (p=0.0005).

CONCLUSIONS

Malignant myoepithelial tumours rarely overexpress ATM but are frequently positive for p53. In benign breast lesions, expression of the MRN complex was more frequently reduced in the myoepithelial than in the luminal epithelial compartment, suggesting different DNA repair capabilities in these two cell types.

Malignant myoepithelial cells are associated with the differentiated papillary structure and metastatic ability of a syngeneic murine mammary adenocarcinoma model

BACKGROUND

The normal duct and lobular system of the mammary gland is lined with luminal and myoepithelial cell types. Although evidence suggests that myoepithelial cells might suppress tumor growth, invasion and angiogenesis, their role remains a major enigma in breast cancer biology and few models are currently available for exploring their influence. Several years ago a spontaneous transplantable mammary adenocarcinoma (M38) arose in our BALB/c colony; it contains a malignant myoepithelial cell component and is able to metastasize to draining lymph nodes and lung.

METHODS

To characterize this tumor further, primary M38 cultures were established. The low-passage LM38-LP subline contained two main cell components up to the 30th subculture, whereas the higher passage LM38-HP subline was mainly composed of small spindle-shaped cells. In addition, a large spindle cell clone (LM38-D2) was established by dilutional cloning of the low-passage MM38-LP cells. These cell lines were studied by immunocytochemistry, electron microscopy and ploidy, and syngeneic mice were inoculated subcutaneously and intravenously with the different cell lines, either singly or combined to establish their tumorigenic and metastatic capacity.

RESULTS

The two subpopulations of LM38-LP cultures were characterized as luminal and myoepithelium-like cells, whereas LM38-HP was mainly composed of small, spindle-shaped epithelial cells and LM38-D2 contained only large myoepithelial cells. All of them were tumorigenic when inoculated into syngeneic mice, but only LM38-LP cultures containing both conserved luminal and myoepithelial malignant cells developed aggressive papillary adenocarcinomas that spread to lung and regional lymph nodes.

CONCLUSION

The differentiated histopathology and metastatic ability of the spontaneous transplantable M38 murine mammary tumor is associated with the presence and/or interaction of both luminal and myoepithelial tumor cell types.

Cytogenetic analysis of myoepithelial cell carcinoma of salivary gland

Myoepithelial cell carcinoma (MCC) of the salivary gland is a rare entity. Here, we describe the karyotype of MCC. The patient was a 53-year-old man, with a rapidly growing lesion of the palate. Despite complete surgical excision, radio- and chemotherapy, the lesion rapidly harboured local and distant metastases leading to the death of the patient, 4 months after the diagnosis. On histological and ultrastructural examination, the primary tumour and the related metastases were composed of oval and spindle cells, with features of myoepithelial cell differentiation reported in the literature. Cytogenetic analysis showed a composite karyotype in the primary tumour: 45-46,XY, +3[cp3]/ 44-45,XY, -17[cp4]/ 46,XY[5]. The lymph-node metastasis was near-triploid and showed a complex karyotype. Our cytogenetic data differ from those described in benign or slowly growing salivary gland tumours showing myoepithelial cell differentiation. It is suggested that highly aggressive tumours might follow a different pathway of malignant transformation.

[Poorly differentiated breast carcinoma with an abundant myoepithelial component: morphologic and immunohistochemical features and mammaglobin gene expression ]

In this report, we describe a case of poorly differentiate myoepithelial cell rich carcinoma in with morphological findings of large poligonal nests with festoon-like pattern sometimes showing central necrosis, reminiscent of a comedo-like pattern and numerous mitoses. Immunohistochemical staining shows positive reaction for cytokeratin AE/1, CAM 5.2, 34 beta E12, vimentin, smooth muscle actin, EMA, S100 protein and oncogene cERB.b2 and negative for estrogen, progesterone, GFAP and chromogranin. Moreover, this carcinoma show the expression of the mammaglobin mRNA, a highly specific marker of breast epithelial cells that it is not expressed in all breast carcinoma.

Analysis of the tumour suppressor genes, FHIT and WT-1, and the tumour rejection genes, BAGE, GAGE-1/2, HAGE, MAGE-1, and MAGE-3, in benign and malignant neoplasms of the salivary glands

AIMS

Molecular genetic changes involved in tumorigenesis and malignant transformation of human tumours are novel targets of cancer diagnosis and treatment. This study aimed to analyse the expression of putative tumour suppressor genes, FHIT and WT-1, and tumour rejection genes, BAGE, GAGE-1/2, MAGE-1, MAGE-3, and HAGE (which are reported to be important in human cancers), in salivary gland neoplasms.

METHODS

Gene expression was analysed by reverse transcription polymerase chain reaction (RT-PCR) in normal salivary gland tissue and 44 benign and malignant salivary gland tumours.

RESULTS

Aberrant FHIT transcripts were found in one of 38 normal salivary glands, three of 28 adenomas, and two of 16 carcinomas. WT-1 mRNA was detectable in two adenomas and five carcinomas. Immunoblotting showed that WT-1 mRNA expression was associated with raised WT-1 protein concentrations. RT-PCR for detection of BAGE, GAGE, and MAGE gene expression was positive in two adenomas and nine carcinomas, but negative in normal salivary gland tissue. HAGE mRNA was found in two normal salivary glands, 11 benign, and eight malignant tumours.

CONCLUSIONS

FHIT mRNA splicing does not appear to be involved in the genesis of salivary gland neoplasms. The upregulation of WT-1 mRNA in tumours of epithelial/myoepithelial phenotype may imply a potential role of WT-1 in the genesis and/or cellular differentiation of these salivary gland tumours. The tumour rejection genes were more frequently, but not exclusively, expressed in malignant salivary gland tumours than in benign neoplasms, although none was suitable as a diagnostic marker of malignancy in salivary gland neoplasms.

Epithelial-myoepithelial carcinoma of the parotid gland-evidence of contrasting DNA patterns in two different histological parts

Epithelial-myoepithelial carcinoma (EMC) is a rare neoplasm arising predominantly in the salivary glands, in particular in the parotid gland. We report the morphological features of an epithelial-myoepithelial carcinoma of the parotid gland with one lymph-node metastasis including a molecular genetic study of this tumor. Immunohistochemical and ultrastructural results confirmed the epithelial-myoepithelial dualism of the carcinoma. The loss of heterozygosity (LOH) analysis revealed different LOH results for the solid and the tubular growth pattern of the primary tumor, but showed identical findings for the solid primary tumor component and the lymph node metastasis which had also a solid appearance. LOH could be demonstrated in the whole primary tumor at D13S217 (13q12) and D18S58 (18q21). In three other microsatellite loci [D9S162 (9p22-p21), D10S251 and D10S541 (surrounding the PTEN/MMAC1 gene on 10q23-q24)], clearly recognizable LOH was found in the solid part and in the metastasis, whereas the tubular component demonstrated only a slight decrease of the same allele. No mutation or methylation of the p16 gene or alteration of the PTEN/MMAC1 gene could be found. Nevertheless, our results provoke a discussion, whether these genetic alterations could be considered as determinants of histologically and prognostically divergent types in EMC.

Myoepithelial mRNA expression profiling reveals a common tumor-suppressor phenotype

A series of myoepithelial cell lines and xenografts derived from benign human myoepithelial tumors of diverse sources (salivary gland, breast, and lung) exhibit common mRNA expression profiles indicative of a tumor-suppressor phenotype. Previously established myoepithelial cell lines and xenografts (HMS-#; HMS-#X) were compared to nonmyoepithelial breast carcinoma cells (MDA-MB-231 and MDA-MB-468, and inflammatory breast carcinoma samples, IBCr, and IBCw), a normal mammary epithelial cell line (HMEC) and individual cases of human breast cancer (zcBT#T), and matched normal human breast tissues (zcBT#N) (overall samples = 22). The global gene expression profile (22,000 genes) of these individual samples was examined using Affymetrix Microarray Gene Chips and subsequently analyzed with both Affymetrix and DChip algorithms. The myoepithelial cell lines/xenografts were distinct and very different from the nonmyoepithelial breast carcinoma cells and the normal breast and breast tumor biopsies. Two hundred and seven specifically selected genes represented a subset of genes that distinguished (P < 0.05) all the myoepithelial cell lines/xenografts from all the other samples and which themselves exhibited hierarchical clustering. Further analysis of these genes revealed increased expression in genes belonging to the classes of extracellular matrix proteins, angiogenic inhibitors, and proteinase inhibitors and decreased expression belonging to the classes of angiogenic factors and proteinases. Developmental genes were also differentially expressed (either over or underexpressed). These studies confirm our previous impression that human myoepithelial cells express a distinct tumor-suppressor phenotype.

Relative paucity of gross genetic alterations in myoepitheliomas and myoepithelial carcinomas of salivary glands

The diagnosis of salivary gland myoepithelioma, an entity with heterogeneous cytomorphology and inconsistent immunophenotype, rests on conventional histology. However, the clinical course cannot be predicted reliably from cytomorphological and immunophenotypic analysis. The present study determined the immunophenotype of a representative series of 12 myoepitheliomas and 21 malignant myoepitheliomas. Among the seven markers tested, antibodies against cytokeratins 5/6, S-100 protein, and vimentin produced the most consistent reactivity profile. Comparative genomic hybridization (CGH) profiles of 12 myoepitheliomas showed chromosomal losses in three of 12 cases. In myoepithelial carcinomas, however, ten of 19 tissues investigated by CGH lacked detectable cytogenetic aberrations. In five cases, aberrations involved chromosome 8, in line with observations in salivary gland carcinomas of other differentiation. One case that was represented in three separately localized manifestations of the disease proved informative as to the relevance of gross aberration for tumour development, as these tumours differed in their CGH profiles. Staining for cytokeratins 5/6 is a useful addition to the established immunohistological marker panel in the work-up of myoepitheliomas, because of its reliable expression in most cases and because it may underline the epithelial nature of the lesion. CGH proved to be of limited value as a diagnostic adjunct; the presence of numerous gross cytogenetic aberrations should raise the suspicion of malignancy. The low frequency of aberrations detectable by CGH in overtly malignant myoepithelial neoplasms suggests that gross cytogenetic alterations were acquired in the course of tumour progression and points to the relevance of genetic changes not resolved by CGH.

A case of myoepithelial carcinoma displaying biallelic inactivation of the tumour suppressor gene APC in a patient with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder caused by mutation of the APC gene. It is characterised by the appearance of hundreds to thousands of colorectal adenomas in adolescence and the subsequent development of colorectal cancer. Various extracolonic malignancies are associated with FAP, including desmoids and neoplasms of the stomach, duodenum, pancreas, liver, and brain. We present a family affected by FAP with an exon 14 APC mutation displaying two rare extracolonic lesions, a hepatoblastoma and a myoepithelial carcinoma. The hepatoblastoma was found in a male patient aged 2 years. The second lesion, a myoepithelial carcinoma of the right cheek, was found in a female patient aged 14 years. Inactivation of the normal APC allele was demonstrated in this lesion by loss of heterozygosity analysis, thus implicating APC in the initiation or progression of this neoplasm. This is the first reported case of this lesion in a family affected by FAP.

Telomere length and telomerase activity in canine mammary gland tumors

OBJECTIVE

To measure telomere length and telomerase activity in naturally occurring canine mammary gland tumors.

SAMPLE POPULATION

27 mammary gland tumor specimens obtained during resection or necropsy and 12 mammary gland tissue specimens obtained from healthy (control) dogs.

PROCEDURE

Telomere length in tissue specimens was measured by use of restriction endonuclease digestion and Southern blot analysis. Telomerase activity was measured by use of a telomeric repeat amplification protocol assay.

RESULTS

Telomere length in mammary gland tumors ranged from 11.0 to 21.6 kilobase pairs (kbp; mean +/- SEM, 14.5+/-0.5 kbp) but did not differ among tumor types. Telomeres in mammary gland tumors were slightly shorter than in normal tissue specimens, but telomere length could not be directly compared between groups, because mean age of dogs was significantly different between groups. Age was negatively correlated with telomere length in control dogs but was not significantly correlated with length in affected dogs. Telomerase activity was detected in 26 of 27 mammary gland tumors and in 4 of 12 normal tissue specimens. However, telomerase activity and telomere length were not correlated in tumor specimens.

CONCLUSIONS AND CLINICAL RELEVANCE

Telomere length is maintained in canine mammary gland tumors regardless of the age of the affected dog. Measurement of telomere length may be a useful tool for monitoring the in vivo effects of telomerase inhibitors in dogs with tumors.

Comparative genomic hybridization analysis of myoepithelial carcinoma of the breast

Although there seems to be a common stem cell for the two epithelial cell types in the breast, the vast majority of breast cancers exhibit a luminal phenotype. Pure myoepithelial carcinomas are rare. We report our findings of genetic alterations in these tumors. We have analyzed 10 cases of pure myoepithelial cell carcinomas using laser capture microdissection and comparative genomic hybridization. The mean number of changes was 2.1 (range 0-4), compared with a mean of 8.6 (range 3.6-13.8) in unselected ductal carcinomas. Common alterations included loss at 16q (3/10 cases), 17p (3/10), 11q (2/10), and 16p (2/10), regions also commonly deleted in ductal carcinomas. The single case in which both pure myoepithelial carcinoma and invasive ductal carcinoma was present showed 2 alterations in the myoepithelial tumor (losses at 17p and 17q), whereas the invasive ductal component showed 15 alterations (5 gains and 9 losses), including loss at 17p. The sharing of 17p loss in myoepithelial and ductal carcinoma is consistent with a common stem cell model in the breast. The relatively few genetic alterations in otherwise aggressive neoplasms suggests that myoepithelial tumors may be a good model for the delineation of genes important in breast tumorigenesis.

Expression of the c-kit protein is associated with certain subtypes of salivary gland carcinoma

The c-Kit protein, a receptor type tyrosine kinase that plays an important role in the development of hematopoietic cells, melanocytes, and germ cells, is expressed in mastocytosis, gastrointestinal stromal cell tumors (GISTs), germ cell tumors, and several other tumors. Gain-of-function mutations in exon 11 and exon 17 have been shown as a mechanism of c-kit activation in some tumors. To study the role of c-kit in salivary gland carcinomas, we analyzed the c-kit protein expression in 79 carcinomas of major and minor salivary glands by immunohistochemistry. Although varying in intensity of staining, c-kit expression was identified very often in adenoid cystic carcinomas (20/25), lymphoepithelioma-like carcinomas (6/6) and myoepithelial carcinomas (2/2), but not in other types of salivary gland carcinoma (0/46), P<0.00001. By DNA sequencing, genetic alteration of c-kit juxtamembrane domain (exon 11) and tyrosine kinase domain (exon 17) was not found in all the three types of salivary carcinoma that had c-kit protein expression. In conclusion, c-kit protein overexpression is involved in the pathogenesis of certain types of salivary gland carcinoma, but mutation of the gene is not the mechanism of c-kit activation.

Cytogenetic analysis of a primary salivary gland myoepithelioma

Myoepithelioma, a rare benign salivary gland neoplasm, is a tumor composed entirely of myoepithelial cells. Unlike pleomorphic adenoma, these tumors lack any ductal epithelial differentiation, and manifest a minor stromal element. Previous cytogenetic and molecular genetic studies have mainly investigated pleomorphic adenomas and reported recurring specific chromosomal alterations at 8q12 and 12q13-q15 regions. The cell origin of these alterations, however, remains speculative. We report the cytogenetic analysis of a parotid myoepithelioma and discuss the putative origin for the cells with cytogenetic alterations. Our analysis shows 12q12 involved in a translocation with a previously unreported partner (1q), and nonrandom del(9)(q22.1q22.3) and del(13)(q12q22). Our results indicate that the myoepithelial cell is the source of those cells with chromosomal alterations, and that myoepithelioma shares 12q alterations reported in a subset of pleomorphic adenomas.

[Expression of c-erbB-2 oncogene and mutation of p53 gene in myoepithelioma and myoepithelial carcinoma]

Expression of c-erbB-2 oncogene and mutant p53 protein were detected immunohistochemically in 14 cases of myoepithelioma and 6 cases of myoepithelial carcinoma of the salivary gland. Five of the 6 myoepithelial carcinomas and nine of the 14 myoepitheliomas were overexpression of c-erbB-2 oncoprotein. The salivary ductal epithelial cells near tumors were overexpression of c-erbB-2 oncoprotein. These results indicate that c-erbB-2 may be an initial oncogene during the histogenesis of myoepithelial tumors. The p53 protein was positive in five cases of the 6 myoepithelial carcinoma, whereas all myoepitheliomas were negative. The results indicate that the mutant p53 gene may play an important role in the carcinogenesis of myoepithelial carcinoma.

Quantitative multivariate analysis of myoepithelioma and myoepithelial carcinoma

The nuclear DNA content and morphologic data of 30 surgical samples (eight normal parotid gland, 12 myoepithelioma, and 10 myoepithelial carcinoma) were analyzed by the IBAS II analysis system. The results suggest that there are relationships between tumor ploidy distribution and prognosis, and that correct pathologic diagnosis can be obtained by the IBAS image system.

Nucleolar organizer regions (NORs) and myoepitheliomas: a comparison with DNA content and clinical course

Nucleolar organizer regions (NOR) were studied in 15 salivary gland myoepitheliomas by an argyrophilic staining technic (AgNOR). The AgNOR data were then compared with flow cytometric DNA content of the neoplasms and also with selected clinicopathologic parameters. We conclude that AgNOR's: (1) do not correlate well with DNA cytometric indices and (2) at best, provide redundant information.

Metastasizing pleomorphic adenoma with myoepithelial cell predominance

The biological behavior of pleomorphic adenomas (mixed tumors) of salivary gland origin is complex. Tumors with benign histologic features may exhibit recurrence and locally aggressive behavior especially after incomplete excision. A small percentage of pleomorphic adenomas have obvious malignant components in epithelial or in both epithelial and mesenchymal components and can metastasize. There are also rare case reports which appear to document typical pleomorphic adenomas of salivary gland with histologically identical visceral and lymph node metastases. Recently myoepithelial cell proliferation has been identified as a possible predictor of aggressive clinical behavior in otherwise histologically benign pleomorphic adenomas. We report such a parotid gland lesion with local recurrence and retroperitoneal spread. DNA-flow cytometry of cells from the paraffin-embedded primary and metastasis showed similar aneuploid populations. Aneuploidy appeared to reflect the malignant potential of this particular pleomorphic adenoma and suggests that DNA-flow cytometry of salivary gland tumors may yield important prognostic information.