Identification of a Novel MAN1A1-ROS1 Fusion Gene Through mRNA-based Screening for Tyrosine Kinase Gene Aberrations in a Patient with Leiomyosarcoma.

BACKGROUND: Soft tissue sarcomas are a heterogeneous group of rare malignant tumors. Advanced soft tissue sarcomas have a poor prognosis, and effective systemic therapies have not been established. Tyrosine kinases are increasingly being used as therapeutic targets for a variety of cancers and soft tissue sarcomas. Although complex karyotype sarcomas typically tend to carry more potentially actionable genetic alterations than do translocation-associated sarcomas (fusion gene sarcomas), based on our database review, we found that leiomyosarcoma and malignant peripheral nerve sheath tumors have lower frequencies of potential targets than other nontranslocation soft tissue sarcomas. We theorized that both leiomyosarcoma and malignant peripheral nerve sheath tumors might be included in any unique translocations. Furthermore, if tyrosine kinase imbalances, especially fusion genes, occur in patients with leiomyosarcomas and malignant peripheral nerve sheath tumors, tyrosine kinase inhibitors might be a drug development target for this sarcoma. In this study, we used a tyrosine kinase screening system that could detect an imbalance in mRNA between 5'- and 3'-sides in tyrosine kinase genes to identify potential novel therapeutic tyrosine kinase targets for soft tissue sarcomas. QUESTIONS/PURPOSES: (1) Are there novel therapeutic tyrosine kinase targets in tumors from patients with soft tissue sarcomas that are detectable using mRNA screening focusing on imbalance expressions between the 5' and 3' end of the kinase domain? (2) Can potential targets be verified by RNA sequencing and reverse transcription PCR (RT-PCR)? (3) Will potential fusion gene(s) transform cells in in vitro assays? (4) Will tumors in mice that have an identified fusion gene respond to treatment with a therapeutic drug directed at that target? METHODS: We used mRNA screening to look for novel tyrosine kinase targets that might be of therapeutic potential. Using functional assays, we verified whether the identified fusion genes would be good therapeutic candidates for soft tissue sarcomas. Additionally, using in vivo assays, we assessed whether suppressing the fusion's kinase activity has therapeutic potential. Study eligibility was based on a patient having high-grade spindle cell and nontranslocation sarcomas, including leiomyosarcoma, malignant peripheral nerve sheath tumor, and high-grade myxofibrosarcoma. Between 2015 and 2019, of the 172 patients with soft tissue sarcomas treated with surgical resection at Juntendo University Hospital, 72 patients had high-grade nontranslocation sarcomas. The analysis was primarily for leiomyosarcoma and malignant peripheral nerve sheath tumors, and there was a limitation of analysis size (reagent limitations) totaling 24 samples at the start of the study. We collected additional samples from a sample bank at the Tokyo Medical and Dental University to increase the number of sarcomas to study. Therefore, in this study, a total of 15 leiomyosarcoma samples, five malignant peripheral nerve sheath tumors samples, and four high-grade myxofibrosarcoma samples were collected to achieve the sample size of 24 patients. To identify tyrosine kinase fusion genes, we designed a NanoString-based assay (NanoString Technologies Inc, Seattle, WA, USA) to query the expression balances regarding transcripts of 90 tyrosine kinases at two points: the 5' end of the kinase domain and within the kinase domain or 3' end of the kinase domain. The tumor's RNA was hybridized to the NanoString probes and analyzed for the expression ratios of outliers from the 3' to 5' end of the kinase domain. Presumed novel fusion events in these positive tumors that were defined by NanoString-based assays were confirmed tyrosine kinase fusion genes by RNA sequencing and confirmatory RT-PCR. Functional analyses consisting of in vitro and in vivo assays were also performed to elucidate whether the identified tyrosine kinase gene fusions were associated with oncogenic abilities and drug responses. RESULTS: We identified aberrant expression ratios regarding the 3' to 5' end of the kinase domain ratios in ROS1 transcripts in a leiomyosarcoma in a 90-year-old woman. A novel MAN1A1-ROS1 fusion gene was identified from her thigh tumor through RNA sequencing, which was confirmed with real-time PCR. In functional assays, MAN1A1-ROS1 rearrangement revealed strong transforming potential in 3T3 cells. Moreover, in an in vivo assay, crizotinib, a ROS1 inhibitor, markedly inhibited the growth of MAN1A1-ROS1 rearrangement-induced transformed cells in a dose-dependent manner. CONCLUSION: We conducted tyrosine kinase screening to identify new therapeutic targets in soft tissue sarcomas. We found a novel MAN1A1-ROS1 fusion gene that may be a therapeutic target in patients with leiomyosarcoma. This study demonstrates that the mRNA screening system may aid in the development of useful therapeutic options for soft tissue sarcomas. CLINICAL RELEVANCE: If novel tyrosine fusions such as MAN1A1-ROS1 fusion can be found in sarcomas from other patients, they could offer avenues for new molecular target therapies for sarcomas that currently do not have effective chemotherapeutic options. Therefore, the establishment of a screening system that includes both genomic and transcript analyses in the clinical setting is needed to verify our discoveries and take the developmental process of treatment to the next step.

Microsatellite instability and mismatch repair protein expressions in lymphocyte-predominant breast cancer.

The frequency of microsatellite instability (MSI) is reportedly extremely low in breast cancer, despite widespread clinical expectations that many patients would be responsive to immune-checkpoint inhibitors (ICI). Considering that some triple-negative breast cancers (TNBC) responded well to ICI in a clinical trial and that a high density of tumor-infiltrating lymphocytes (TILs) is frequently observed in other cancers with high levels of microsatellite instability (MSI-H), we hypothesized that some TNBC with a high density of TILs would be MSI-H. Medullary carcinoma (MedCa) of the breast, a rare histological type, is characterized by a high density of TILs. Considering that MedCa of the colon is often MSI-H, we suspected that MedCa in breast cancer might also include MSI-H tumors. Therefore, we conducted MSI tests on such breast cancers with a high density of TILs. The MSI status of 63 TIL-high TNBC and 38 MedCa tumors, all from Asian women who had undergone curative surgery, were determined retrospectively. DNA mismatch repair (MMR) proteins and PD-L1 expression were also investigated immunohistochemically. All samples were microsatellite stable, being negative for all microsatellite markers. TIL-high TNBC with low MLH1 protein had higher levels of PD-L1 in stromal immune cells (P = .041). MedCa tumors showed significantly higher PD-L1 expression in immune cells than in TIL-high TNBC (<.001). We found that MSI-H tumors were absent in TIL-high breast cancers. Examination of MMR proteins, not a purpose of Lynch syndrome screening, may merit further studies to yield predictive information for identifying patients who are likely to benefit from ICI.

PTCH1 mutation is a frequent event in oesophageal basaloid squamous cell carcinoma.

Basaloid squamous cell carcinoma (BSCC) is a rare and poorly differentiated variant of typical squamous cell carcinoma, and is characterised in part by activation of the Wnt signalling pathway. We previously demonstrated that constitutive activation of the Wnt signalling pathway by epigenetic silencing of secreted frizzled-related protein 4 (SFRP4) is observed in this tumour. Increasing evidence shows that the Wnt signalling pathway cross-talks with other developmental pathways, including the Hedgehog (HH) pathway. The HH pathway is stimulated by inactivating mutations of PTCH1, which have a well-described oncogenic role in basal cell carcinoma (BCC) of the skin. We employed polymerase chain reaction followed by direct sequencing to detect inactivating mutations of PTCH1 using archival tissue samples of 30 oesophageal BSCCs. The frequency of PTCH1 mutation was compared to that of Wnt component genes that we reported previously. We found PTCH1 mutations in 53.3% (16/30) of cases, revealing T1195S as a hotspot mutation. This frequency is quite high for cancers other than BCC of the skin, and PTCH1 mutations were almost mutually exclusive with mutations in APC, Axin1 and Axin2. Considering the fact that activation of Wnt signalling via down-regulation of APC and SFRP5 due to promoter methylation is observed in BCC of the skin, Wnt signalling activation in oesophageal BSCC might be a secondary effect of the PTCH1-inactivating mutations. These findings suggest that the HH and Wnt pathways coordinately contribute to tumourigenesis in oesophageal BSCC. Furthermore, this study provides a potential therapeutic application for HH pathway inhibitors in oesophageal BSCC with highly malignant potential.

Distinct Clinicopathologic Features and Possible Pathogenesis of Localized ALK-positive Histiocytosis of the Breast.

Anaplastic lymphoma kinase (ALK)-positive histiocytosis is a rare emerging entity characterized by systemic or localized proliferation of histiocytes harboring ALK rearrangements. Breasts are reportedly affected by ALK-positive histiocytosis. Here, we evaluated 2 localized cases of breast ALK-positive histiocytosis through a comprehensive clinicopathologic, molecular, and genomic analysis to further delineate this entity and better understand its pathogenesis. The cases involved 2 undiagnosed ALK-positive spindle-cell breast lesions. Both cases were Asian women aged 30s to 40s who underwent excisions for asymptomatic breast masses. Macroscopically, both lesions were well-circumscribed, solid masses. Microscopically, both lesions were predominantly composed of fascicles with uniform, bland spindle cells, admixed with epithelioid histiocyte-like cells and lymphoid aggregates. Immunohistochemically, the spindle and epithelioid cells coexpressed ALK and histiocytic markers (eg, CD68, CD163). Genetically, both lesions harbored KIF5B-ALK, confirmed by fluorescence in situ hybridization and polymerase chain reaction-direct sequencing analyses. Combining these results, both cases were successfully diagnosed as ALK-positive histiocytosis. Furthermore, no common or previously annotated somatic alterations were identified by whole-exome sequencing. One case harbored clonal immunoglobulin gene rearrangements according to the polymerase chain reaction-based BIOMED-2 protocol. Therefore, ALK-positive histiocytosis can be accurately diagnosed through a combination of morphologic, immunohistochemical, and molecular analyses. In this entity, breast cases may have distinct clinicopathologic features: Asian women aged 30s to 40s, asymptomatic masses, and predominant spindled morphology. For pathogenesis, ALK rearrangements could be the driver alteration, and a subset of ALK-positive histiocytosis may harbor a lymphoid lineage. These findings can be utilized to improve the diagnosis of ALK-positive histiocytosis and better understand its pathogenesis.

Molecular Characteristics of Lymphocyte-predominant Triple-negative Breast Cancer.

BACKGROUND/AIM: Tumor-infiltrating lymphocytes (TILs) are considered a prognostic marker for triple-negative breast cancer (TNBC). Immune checkpoint inhibitor (ICI)-based treatments are more effective for tumors with PD-L1-positive TILs, suggesting crucial roles of TILs in the local tumor immunity. However, factors attracting TILs are still largely unknown. Focusing on tumor antigenicity, we examined TNBC samples to identify the characteristics of TIL-high tumors. PATIENTS AND METHODS: Nine treatment-naïve TNBCs (TIL-high: five, TIL-low: four) were subjected to next-generation sequencing (NGS). Loss of heterozygosity (LOH) of PTEN was also analyzed. RESULTS: A variety of copy number variations were observed, and no genes differed significantly between TIL-high and -low groups. However, PTEN loss was more frequently observed in the TIL-high group: 60% compared to 25% in TIL-low tumors. NGS correlated well with LOH analysis in identifying PTEN loss. All three tumors with PTEN loss in the TIL-high group showed high PD-L1. All nine samples were microsatellite-stable. CONCLUSION: Frequent PTEN loss and high expression of PD-L1 in TIL-high TNBC suggest that PTEN mutation may be a biomarker for ICIs.

KCTD12 is negatively regulated by Kit in gastrointestinal stromal tumors.

Our group has previously demonstrated that pfetin, encoded by the KCTD12 gene, is a strong prognostic biomarker for gastrointestinal stromal tumors (GISTs). However, the underlying mechanisms that control pfetin expression remain unknown. To elucidate the regulatory mechanisms of KCTD12 in GIST, in addition to a possible association between KCTD12 alterations and protein expression, we examined 76 patients with GISTs for KCTD12 mutations by PCR-direct sequence, and compared these results with clinicopathologic data. The function of pfetin in GIST progression was also revealed using GIST T1 cells. In this series, pfetin expression was not observed in 15 cases, and loss of pfetin expression was associated with higher mitotic rate (>5/50HPFs: p = 0.029). There was also a trend between presence of necrosis and loss of pfetin expression but this was not statistically significant (p = 0.09). KCTD12 mutations were frequently observed in 22 out of 76 GISTs (28.9%); however, they did not affect protein expression and were not associated with patients' prognosis. KCTD12 in vitro knockdown resulted in the accelerated growth of GIST T1 cells, confirming that pfetin functions as a tumor suppressor. KIT knockdown significantly inhibited cellular growth and upregulated the expression of pfetin at both the mRNA and protein level. These findings suggest that GISTs with loss of pfetin expression has proliferative advantage and that higher pfetin expression in GISTs may be indicative of lower expression levels of KIT. This relationship confirms that pfetin is a useful prognostic marker in GISTs.

Pneumothorax caused by cystic and nodular lung metastases from a malignant uterine perivascular epithelioid cell tumor (PEComa).

Perivascular epithelioid cell tumors (PEComas) are mesenchymal neoplasms with immunoreactivity for both melanocytic and smooth muscle markers. PEComas occur at multiple sites, and malignant PEComas can undergo metastasis, recurrence and aggressive clinical courses. Although the lung is a common metastatic site of PEComas, they usually appear as multiple nodules but rarely become cystic or cavitary. Here, we describe a female patient whose lungs manifested multiple cystic, cavity-like and nodular metastases 3 years after the resection of uterine tumors tentatively diagnosed as epithelioid smooth muscle tumors with uncertain malignant potential. This patient's subsequent pneumothorax necessitated video-assisted thoracoscopic surgery, and examination of her resected lung specimens eventually led to correcting the diagnosis, i.e., to a PEComa harboring tuberous sclerosis complex 1 (TSC1) loss-of-heterozygosity that originated in the uterus and then metastasized to the lungs. The administration of a gonadotropin-releasing hormone analogue later stabilized her clinical course. To the best of our knowledge, the present case is the first in the literature that associates PEComas with a TSC1 abnormality. Additionally, the pulmonary manifestations, including imaging appearance and pneumothorax, somewhat resembled those of lymphangioleiomyomatosis, a representative disease belonging to the PEComa family. Although PEComas are rare, clinicians, radiologists and pathologists should become aware of this disease entity, especially in the combined clinical setting of multiple cystic, cavity-like, nodular lesions on computed tomography of the chest and a past history of the tumor in the female reproductive system.

Expression of adipophilin in gastric epithelial neoplasia is associated with intestinal differentiation and discriminates between adenoma and adenocarcinoma.

Adipophilin, a lipid droplet-associated protein that regulates lipid droplet structure and formation, is expressed in a wide variety of tumors. The aims of this study were to evaluate the frequency and distribution pattern of adipophilin expression in gastric epithelial neoplasia and to correlate these variables with clinicopathological features and the mucin phenotype. We retrospectively examined 159 cases of gastric epithelial neoplasia, which were classified according to the Vienna classification system as 52 noninvasive low-grade adenoma (category 3), 65 noninvasive high-grade neoplasia (category 4), and 42 invasive neoplasia (category 5). Immunohistochemistry for adipophilin was performed, and phenotypic marker expression was determined by immunohistostaining with MUC2, MUC5AC, CD10, MUC6, and villin. Adipophilin was expressed in 41 of the 52 (79 %) category 3 cases, in 42 of the 65 (65 %) category 4 cases, and in 23 of the 42 (55 %) category 5 cases. Expression of adipophilin was only present in lesions with complete or incomplete intestinal phenotypes. Adipophilin was expressed more frequently in the surface epithelium in category 3, whereas there was a stepwise increase in cryptal staining of adipophilin from category 3 to category 5. In conclusion, adipophilin expression is closely related to the intestinal differentiation of the tumor. The pattern of immunostaining for adipophilin might be a useful new marker for discriminating adenomas from adenocarcinomas.

In Japanese patients with papillary thyroid carcinoma, TERT promoter mutation is associated with poor prognosis, in contrast to BRAF V600E mutation.

The prognostic value of BRAF V600E and TERT promoter mutation in papillary thyroid carcinoma (PTC) is controversial. We examined alterations in BRAF V600E and TERT promoter by PCR-direct sequencing in PTC of 144 Japanese patients. Alternative lengthening of telomeres was examined as another mechanism of telomere maintenance by immunohistochemical staining for ATRX and DAXX. Of the clinicopathological characteristics, regional lymph node metastasis, extra-thyroid extension, multifocality/intrathyroidal spread, and advanced stage (III/V) were associated with shorter disease-free survival rate (DFSR). TERT promoter mutation was found in eight patients (6 %), and this was significantly associated with total thyroidectomy, multifocality/intrathyroidal spread, lymph node metastasis and advanced stage. The BRAF V600E mutation was found in 53 patients (38.2 %) but was not associated with any clinicopathological factors. TERT mutations were not correlated with BRAF V600E mutation status. TERT mutation-positive tumors (TERT+) showed lower DFSR than BRAF V600E -mutation-positive tumors (BRAF V600E +), and TERT+/BRAF V600E + tumors showed lower DFSR than BRAF V600E + tumors. No cases showed loss of ATRX/DAXX expression by immunohistochemistry. TERT promoter mutations showed a lower prevalence in our series and appeared to be associated with aggressive behavior. In PTCs, telomerase activation by TERT promoter mutation might be more important than alternative lengthening of telomeres.

TERT promoter mutations are rare in bone and soft tissue sarcomas of Japanese patients.

Recurrent hot-spot mutations in the telomerase reverse transcriptase (TERT) promoter have been reported in various types of tumor. In several tumor types, TERT promoter mutations are associated with poor clinical outcomes. TERT promoter mutations are reported to be rare in soft tissue tumors, with the exception of myxoid liposarcoma (MLS). Our previous study reported that TERT promoter mutations occurred in a subset of solitary fibrous tumors (SFTs) and were associated with adverse clinical outcomes in Japanese individuals. The site-specific frequency (e.g. central nervous or soft tissue origin) of TERT promoter mutations in our SFT cases appeared to be different from previously reported values in a European population. These findings prompted the present study to elucidate the potential role of ethnic background in the different frequencies of TERT promoter mutations in bone and soft tissue sarcomas. In the present study, TERT promoter mutations were examined in 180 cases of bone and soft tissue sarcomas. TERT promoter region mutations were identified in 10 cases [5 SFTs, 3 MLSs, 1 undifferentiated pleomorphic sarcoma (UPS) and 1 malignant granular cell tumor]. All mutations were C228T. The frequencies of TERT promoter mutation in MLS and UPS were 23.1 (3/13) and 5% (1/20), respectively. Only 1/5 patients with TERT-mutated tumors experienced local recurrence or distant metastasis. The present study revealed the first case of a malignant granular cell tumor with a TERT promoter mutation and revealed that the frequency of TERT promoter mutations in MLSs of Japanese patients is lower compared with that reported in German patients, providing evidence of a possible ethnic difference in the frequency of TERT promoter mutations.

Sarcomatous transformation of EGFR and TP53 mutation-positive metastatic adenocarcinoma of the lungs, masquerading as a primary pleomorphic sarcoma of the proximal femur.

We investigated a case of metastatic adenocarcinoma of the lungs at the left proximal femur, masquerading as a primary pleomorphic sarcoma. A 72-year-old woman presented with pain in her left thigh in conjunction with a mass that had been gradually growing over a few months. She was being treated with gefitinib for lung adenocarcinoma positive for the epidermal growth factor receptor (EGFR) mutation L858R, and had multiple bone metastases. The lung adenocarcinoma and metastases had stabilized with the treatment. The metastatic lesions in the bone had also received radiation; however, a tumor in the proximal femur kept growing despite treatment. A biopsy specimen from the proximal femur revealed the proliferation of spindle-shaped cells without an epithelial glandular component. The patient underwent en bloc resection of the proximal femur that was replaced by prosthesis. Histologically, the resected tumor was entirely composed of pleomorphic cells and tumor giant cells exhibiting no apparent glandular structures. Tumor cells were diffusely positive for p53 and focally positive for epithelial markers and EGFR, but were negative for thyroid transcription factor-1, suggesting an initial diagnosis of primary pleomorphic sarcoma. Genetic examination revealed mutations in EGFR and p53 that were of the same type as the lung tumor, leading to the final diagnosis of the femoral mass as a sarcomatous transformation of metastatic lung adenocarcinoma. However, secondary genetic alterations that might explain the acquired resistance to gefitinib could not be found in the proximal femoral tumor. The patient remains alive and the remaining lesions are well controlled.

Distinct clinicopathological features of NAB2-STAT6 fusion gene variants in solitary fibrous tumor with emphasis on the acquisition of highly malignant potential.

The impact of NGFI-A binding protein 2 (NAB2)-signal transducer and activator of transcription 6 (STAT6) fusion on the biological behavior and the mechanism of acquisition of malignant phenotype in solitary fibrous tumor (SFT) is not well understood. We examined variations of the NAB2-STAT6 fusion gene in 40 cases of SFT using formalin-fixed, paraffin-embedded tissues and secondary genetic alterations of tumor protein p53 (TP53),, platelet-derived growth factor receptor, ß polypeptide (PDGFRB), and telomerase reverse transcriptase (TERT) promoters. These gene variations were compared with the clinicopathological features. The 2-year and 5-year disease-free survival rates (DFSRs) were 91% and 83%, respectively. All 40 samples demonstrated nuclear staining for STAT6, including CD34-negative cases. Moreover, p53-positive staining was associated with a lower DFSR and was significantly associated with higher Ki-67 label index, higher mitotic rate (mitosis, >4/high-power field), and the presence of nuclear atypia/pleomorphism. NAB2-STAT6 fusions were detected in all of the cases; the NAB2 exon 4-STAT6 exon 2, the most common genotype, appeared in 18 cases, which was associated with thoracic tumor location and the less aggressive phenotype. In contrast, tumors with NAB2 exon 6-STAT6 exon 16/18 demonstrated an aggressive phenotype. Mutations in TP53 and PDGFRB were detected in 2 and 3 cases respectively, and these occurred in a mutually exclusive fashion. TERT promoter hot spot mutations were observed in 5 cases, which were associated with shorter DFSR. Two dedifferentiated SFT cases harbored both TP53 and TERT promoter mutations. TP53 mutations, which result in its overexpression, in combination with TERT promoter mutations seem to play an important role in the dedifferentiation process.

A case of (123)I-MIBG scintigram-negative functioning pheochromocytoma: immunohistochemical and molecular analysis with review of literature.

A 70-year-old Japanese woman was referred to our hospital due to hyperhidrosis and rapid weight loss of 10 kg in a month. A lump measuring 26 mm in diameter was detected in the left adrenal gland by computed tomography. Biochemical tests showed high levels of serum and urinary norepinephrine and epinephrine. However, a (123)I-MIBG scintigram failed to detect any accumulation in the left adrenal tumor. A left adrenalectomy was performed post clinical diagnosis of (123)I-MIBG negative pheochromocytoma. Microscopically, the tumor exhibited pheochromocytoma compatible features. Immunohistochemical analysis revealed low expression of VMAT1 in the tumor compared to the normal, surrounding tissue. To test for a possible genetic alteration of the monoamine transporter genes, we performed whole-exome sequencing of the VMAT1, VMAT2, and NET genes in the tumor. No significant base sequence substitution or deletion/insertion was found in any transporter. This suggests that MIBG negativity is caused by a change that is independent of the base sequence abnormalities, such as an epigenetic change. Furthermore, a retrospective literature review of (123)I-MIBG negative-scintigraphy cases indicates that a negative finding in the (123)I-MIBG scintigram is frequently associated with metastatic pheochromocytomas or SDHB mutations. However, a SDHB/D gene mutation has not been identified in the reported case. Although the patient needs careful monitoring following the surgery, to date she has been disease free for 12 months. This study could not find clear reasons for negative conversion, however, investigations of the negative conversion mechanism might reveal significant insights towards the improvement of patient survival.

A case of dedifferentiated solitary fibrous tumor of the thoracic cavity.

Solitary fibrous tumors (SFTs), initially observed in the pleura, were later found to develop in almost any extrapleural site. Dedifferentiation within SFTs, a rare phenomenon, was characterized only recently, although it was previously described in soft tissue and bone tumors. We report a case of dedifferentiated SFT arising in the right pleura of a 69-year-old man. Computed tomography revealed a huge mass in the thoracic cavity. The tumor contained an area with a high degree of calcification and was heterogeneously enhanced. Macroscopically, the resected tumor was 175×145×135 mm in size. Morphologically and immunohistochemically, this was comprised of a typical SFT juxtaposed to a high-grade component including an osteosarcomatous component. These were sharply demarcated by thin fibrous septa. Furthermore, NAB2-STAT6 fusion transcripts were detected by reverse-transcriptase polymerase chain reaction in both conventional and high-grade components, supporting the concept of a dedifferentiation process in this tumor.

A case of low-grade fibromyxoid sarcoma with unusual central necrosis in a 77-year-old man confirmed by FUS-CREB3L2 gene fusion.

INTRODUCTION: Low-grade fibromyxoid sarcoma (LGFMS) is a rare soft tissue tumor typically affecting young to middle-aged adults. Despite its otherwise benign histologic appearance and indolent nature, it can display fully malignant behavior, and recurrence and metastasis can occur even decades after diagnosis. PRESENTATION OF CASE: Herein, we report a case of LGFMS in the buttock of a 77-year-old man. Magnetic resonance imaging uncovered a well-demarcated tumor measuring 27×20mm with a slightly high intensity on T1-weighted images (WIs) and heterogeneously high intensity on T2-WIs. Histologically, the tumor was composed of bland spindle-shaped cells in a whorled growth pattern with alternating fibrous and myxoid stroma. The tumor stroma was variably hyalinized with arcades of curvilinear capillaries and arterioles with associated perivascular fibrosis. Unusual histology, such as central necrosis and cystic formation, was also noted. Reverse transcription polymerase chain reaction from a formalin-fixed, paraffin-embedded biopsy specimen revealed a FUS-CREB3L2 gene fusion (exon6/int/exon5), leading to the diagnosis of LGFMS. DISCUSSION: To the best of our knowledge, this is the second oldest patient to be diagnosed with LGFMS. CONCLUSION: At the time of this report, the patient was alive with no evidence of the disease 4 months after diagnosis without any adjuvant therapy.

A case of dedifferentiated solitary fibrous tumor in the pelvis with TP53 mutation.

Solitary fibrous tumors (SFTs), initially observed in the pleura, were later found to develop in almost any extrapleural site. Dedifferentiation within SFTs was characterized only recently. We report a case of dedifferentiated SFT arising within the pelvis of a 70-year-old Japanese woman. Macroscopically, the resected tumor measured 17 × 17 × 13 cm. Histologically, the tumor displayed distinct heterologous osteosarcomatous and chondrosarcomatous components on a background of conventional SFT. Immunohistochemistry uncovered a loss of CD34 expression in the dedifferentiated area, whereas the nuclear expression of signal transducer and activator of transcription-6 (STAT6) and NGFI-A-binding protein 2 (NAB2) was maintained in both components. The p53 mutation 158 CGC > CAC (A158H) was found only in the dedifferentiated component. Furthermore, a fusion gene of NAB2(exon6)-STAT6(exon18) was detected in both the conventional and dedifferentiated components. The patient died of the disease 4 months after surgery. This case identifies a possible role of p53 dysfunction in the dedifferentiation process of SFT as reported in other sarcomas.

Deeply located low-grade fibromyxoid sarcoma with FUS-CREB3L2 gene fusion in a 5-year-old boy with review of literature.

BACKGROUND: Low-grade fibromyxoid sarcoma (LGFMS) is a rare soft tissue tumor typically affecting young to middle-aged adults. Despite its otherwise benign histologic appearance and indolent nature, it can have fully malignant behavior, and recurrence and metastasis may occur even decades later. CASE HISTORY: We report a case of LGFMS in the left lower leg of a 5-year-old Japanese boy. A magnetic resonance imaging (MRI) uncovered a well-demarcated intra-gastrocnemial tumor measuring 27 × 20 mm with a slightly high intensity on T1WI and heterogeneously high intensity on T2WI. Histologically, the tumor was composed of bland spindle-shaped cells with a whorled growth pattern. The tumor stroma was variably hyalinized and fibromyxoid with arcades of curvilinear capillaries and arterioles with associated perivascular fibrosis. Although LGFMS is known to affect children under 18 years of age, it is extremely rare in infants and children under 5 years of age. Despite the young age, this patient was accurately diagnosed by the typical histology and the detection of a FUS-CREB3L2 gene fusion. CONCLUSION: Although LGFMS in children tends to be located superficially, this case presented with an intramuscular tumor in the region of the gastrocnemius. To the best of our knowledge, this is the first case of deep LGFMS arising in a child younger than 5 years of age. The patient is still alive with no evidence of the disease 4 months after diagnosis. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_163.

A case of bilateral renal cell carcinoma associated with long-term dialysis showing false-positive immunoreactivity for TFE3 as Xp11 translocation renal cell carcinoma.

Renal carcinomas associated with Xp11.2 translocations/transcription factor 3 (TFE3) gene fusion (Xp11 translocation RCC) are a rare subtype of renal cell carcinoma. A middle-aged Japanese man, who had a medical history of dialysis for more than 12 years, had bilateral renal cancers with a background of acquired cystic disease of the kidney and remarkable deposition of calcium oxalate in the tumorous area. The right renal tumor showed papillary architecture of clear cells with diffuse and strong immunoreactivity for TFE3 and focal and weak positivity for cathepsin K, suggesting a possibility of Xp11 translocation RCC. However, RT-PCR failed to detect any type of the reported fusion genes involving TFE3. Thus, the sample was sent for a TFE3 break-apart FISH assay in a renal tumor consultation service, which reported no evidence of TFE3 gene rearrangement. The right renal tumor was finally diagnosed as papillary renal cell carcinoma with cystic change. We report here a case of bilateral renal cell carcinoma in a patient undergoing long-term dialysis, which showed false-positive immunoreactivity for TFE3 immunostaining. Titration of TFE3 immunohistochemical staining (IHC) should be performed and cross-referenced with the FISH or RT-PCR results to avoid the misinterpretation of TFE3 IHC results.