Novel ZC3H7B‐BCOR,MEAF6‐PHF1, and EPC1‐PHF1 fusions in ossifying fibromyxoid tumors—molecular characterization shows genetic overlap with endometrial stromal sarcoma

PHF1 gene rearrangements have been recently described in around 50% of ossifying fibromyxoid tumors (OFMT) including benign and malignant cases, with a small subset showing EP400‐PHF1 fusions. In the remaining cases no alternative gene fusions have been identified. PHF1‐negative OFMT, especially if lacking S100 protein staining or peripheral ossification, are difficult to diagnose and distinguish from other soft tissue mimics. In seeking more comprehensive molecular characterization, we investigated a large cohort of 39 OFMT of various anatomic sites, immunoprofiles and grades of malignancy. Tumors were screened for PHF1 and EP400 rearrangements by FISH. RNA sequencing was performed in two index cases (OFMT1, OFMT3), negative for EP400‐PHF1 fusions, followed by FusionSeq data analysis, a modular computational tool developed to discover gene fusions from paired‐end RNA‐seq data. Two novel fusions were identified ZC3H7B‐BCOR in OFMT1 and MEAF6‐PHF1 in OFMT3. After being validated by FISH and RT‐PCR, these abnormalities were screened on the remaining cases. With these additional gene fusions, 33/39 (85%) of OFMTs demonstrated recurrent gene rearrangements, which can be used as molecular markers in challenging cases. The most common abnormality is PHF1 gene rearrangement (80%), being present in benign, atypical and malignant lesions, with fusion to EP400 in 44% of cases. ZC3H7B‐BCOR and MEAF6‐PHF1 fusions occurred predominantly in S100 protein‐negative and malignant OFMT. As similar gene fusions were reported in endometrial stromal sarcomas, we screened for potential gene abnormalities in JAZF1 and EPC1 by FISH and found two additional cases with EPC1‐PHF1 fusions. © 2013 Wiley Periodicals, Inc.     

Ossifying fibromyxoid tumor: morphology,genetics, and differential diagnosis

Ossifying fibromyxoid tumor (OFMT) is a soft tissue neoplasm of uncertain differentiation and intermediate (rarely metastasizing) biologic potential, with typical morphologic features, of an encapsulated, lobulated tumor comprising uniform polygonal cells within fibromyxoid stroma, which is surrounded by or contains metaplastic bone, classically as a peripheral rim of lamellar bone. Ossifying fibromyxoid tumor can arise at almost any site, although most frequently occurs within the extremities and trunk. Although most behave in a benign fashion, tumors can rarely show atypical or malignant features. It is now established that OFMTs represent translocation-associated tumors, with up to 85% associated with recurrent gene rearrangements, mostly involving the PHF1 gene (including in typical, atypical, and malignant neoplasms), with EP400-PHF1 in approximately 40% of tumors, and ZC3H7B-BCOR, MEAF6-PHF1, and EPC1-PHF1 fusions also described. Correct diagnosis is clinically important to ensure correct treatment and prognostication, both to avoid overdiagnosing OFMT as a malignant neoplasm such as osteosarcoma and also because of the propensity for aggressive behavior in a small number of OFMT. We review OFMT, with emphasis on the morphologic spectrum, recent molecular genetic findings, and the differential diagnosis.     

Ossifying fibromyxoid tumor: Fine‐needle aspiration cytology findings of a rare soft tissue neoplasm

Ossifying fibromyxoid tumors (OFMTs) are rare tumors of uncertain origin and intermediate (rarely metastasizing) biologic potential, with characteristic morphology of an encapsulated tumor containing polygonal cells in an abundant fibromyxoid matrix surrounded by a peripheral layer of metaplastic lamellar bone. FNA cytology of OFMT has not been sufficiently reported and till date cytological features of only seven cases have been reported so far. We report another case of OFMT in a 55‐year‐old female presenting with longstanding swelling in thigh. On fine‐needle aspiration, a tumor with moderate cellularity and myxoid areas was seen; coupled with compatible radiological findings, a diagnosis of OFMT was suggested. Establishing a correct diagnosis is important as although OFMT is benign in nature, local recurrences or rarely distant metastasis have been seen of this tumor. Hence, a high degree of suspicion with radiological correlation is of utmost importance for identification of this entity.     

Atypical ossifying fibromyxoid tumor unusually located in the mediastinum: report of a case showing mosaic loss of INI-1 expression

Ossifying fibromyxoid tumor (OFMT) is a rare soft tissue tumor. OFMT mostly arises in subcutaneous tissue or skeletal muscle of the extremities and is extremely unusual in the mediastinum. OFMT is classified as typical, atypical, or malignant as tumor aggressiveness increases. Herein, we presented a case of atypical OFMT that developed in the mediastinum of a 43-year-old woman. Because of its predominant hypercellular area and some tumor cells with high nuclear grade, it was not a typical OFMT. However, it did not have a sufficient number of mitotic figures to be classified as malignant. Hence, we classified it as atypical OFMT with some apparent characteristic features of OFMT, such as the presence of spicules of bone at the periphery of the tumor. Upon immunohistochemistry, it was positive for vimentin, S-100 protein, and CD10, which was consistent with a diagnosis of OFMT. Particularly noteworthy was the mosaic loss of INI-1 expression. Some OFMT and other exceptionally rare tumors have been reported to exhibit mosaic INI-1 loss. Inactivation of INI-1 gene and deregulation of PHF1 gene are thought to be involved in tumorigenesis of OFMT. Therefore, we speculated that the mosaic loss of INI-1 observed in the present case might also be related to a kind of abnormality of INI-1 as was reported previously.     

Variant WWTR1 gene fusions in epithelioid hemangioendothelioma—A genetic subset associated with cardiac involvement

The genetic hallmark of epithelioid hemangioendothelioma (EHE) is a recurrent WWTR1‐CAMTA1 fusion, which is present in most cases bearing a conventional histology. A subset of cases is characterized by a distinct morphology and harbors instead of YAP1‐TFE3 fusion. Nevertheless, isolated cases lack these canonical fusions and remain difficult to classify. Triggered by an index case of a left atrial mass in a 76‐year‐old female with morphologic features typical of EHE, but which showed a WWTR1‐MAML2 fusion by targeted RNA sequencing, we searched our files for similar cases displaying alternative WWTR1 fusions. A total of 6 EHE cases were identified with variant WWTR1 fusions, four of them presenting within the heart. There were three females and three males, with a wide age range at diagnosis (21‐76 years, mean 62, median 69). The four cardiac cases occurred in older adults (mean age of 72, equal gender distribution); three involved the left atrium and one the right ventricle. One case presented in the vertebral bone and one in pelvic soft tissue. Microscopically, all tumors had morphologic features within the spectrum of classic EHE; two of the cases appeared overtly malignant. All cases were tested by FISH and four were investigated by targeted RNA sequencing. Two tumors harbored WWTR1‐MAML2 fusions, one WWTR1‐ACTL6A, and in three cases, no WWTR1 partner was identified. Of the four patients with follow‐up, two died of disease, one was alive with lung metastases, and the only patient free of disease was s/p resection of a T11 vertebral mass. Our findings report on additional genetic variants involving WWTR1 rearrangements, with WWTR1‐MAML2 being a recurrent event, in a small subset of EHE, which appears to have predilection for the heart.     

Nerve cell markers in ossifying fibromyxoid tumour of soft parts

Reported herein are two benign ossifying fibromyxoid tumors (OFMTs) of the soft tissues in axilla and terminal phalanx respectively. Both cases on immunohistochemistry (IHC) showed reactivity for vimentin, S-100 protein and glial fibrillary acidic protein (GFAP) antibodies. In addition, a focal/diffuse strong positivity for neurofilament (NF) and neuron specific enolase (NSE) was observed. Electron microscopy in one instance revealed abundant intermediate filaments, primitive cell junctions and a focally present external lamina. In the light of nerve cell differentiation of these tumors and the similarity of IHC profile and EM features of OFMT to a poorly differentiated malignant peripheral nerve sheath tumor (MPNST); it is suggested that OFMT is a variably differentiated PNST rather than a simple Schwannian neoplasm as is believed.     

Gene fusion analysis in renal cell carcinoma by FusionPlex RNA‐sequencing and correlations of molecular findings with clinicopathological features

Translocation renal cell carcinoma (tRCC) affects younger patients and often presents as advanced disease. Accurate diagnosis is required to guide clinical management. Here we evaluate the RNA‐sequencing FusionPlex platform with a 115‐gene panel including TFE3 and TFEB for tRCC diagnosis and correlate molecular findings with clinicopathological features. We reviewed 996 consecutive RCC cases from our institution over the preceding 7 years and retrieved 17 cases with histological and immunohistochemical features highly suggestive of either TFE3 (n = 16) or TFEB (n = 1). Moderate to strong labeling for TFE3 was present in 15 cases; two cases with weak TFE3 expression were melan‐A or cathepsin‐K positive. RNA‐sequencing detected gene rearrangements in eight cases: PRCC‐TFE3 (3), ASPSCR1‐TFE3 (2), LUC7L3‐TFE3 (1), SFPQ‐TFE3 (1), and a novel SETD1B‐TFE3 (1). FISH assays of 11 tumors verified six positive cases concordant with FusionPlex analysis results. Two other cases were confirmed by RT‐PCR. FusionPlex was superior to FISH by providing precise breakpoints for tRCC‐related genes in a single assay and allowing identification of both known and novel fusion partners, thereby facilitating clinicopathological correlations as fusion partners can influence tumor appearance, immunophenotype, and behavior. Cases with partner genes PRCC and novel partner SETD1B were associated with prominent papillary architecture while cases with partner genes ASPSCR1 and LUC7L3 were associated with a predominantly nested/alveolar pattern. The case with SFPQ‐TFE3 fusion was characterized by biphasic morphology mimicking TFEB‐like translocation RCC. We recommend FusionPlex analysis of RCC in patients under age 50 or when the histologic appearance suggests tRCC.     

Ossifying fibromyxoid tumor: invariable ultrastructural features and diverse immunophenotypic expression

Ossifying fibromyxoid tumor (OFMT) is a rare enigmatic soft tissue tumor, the origin of which is still uncertain. The authors report on 3 cases of OFMT arising in the trunk and head and neck regions of adults. Two recurred and one was suspected to have metastasis. All tumors consisted of multiple nodules, in which round or polygonal tumor cells were arranged in sheets or cords within a fibromyxoid background. Characteristic shell-like bone tissues were recognized in all tumors. Based on the grading system proposed by Folpe et al., 2 cases were designated as malignant OFMT and 1 as typical. In addition to S-100 protein, cytokeratin and neuronal markers (neurofilament, CD56 or CD57) were detected in 1 and 2 tumors, respectively. The salient and invariable ultrastructural features included reduplicated basal laminas, which seem to be crucial for the diagnosis.     

Ossifying Fibromyxoid Tumor: Invariable Ultrastructural Features and Diverse Immunophenotypic Expression

Ossifying fibromyxoid tumor (OFMT) is a rare enigmatic soft tissue tumor, the origin of which is still uncertain. The authors report on 3 cases of OFMT arising in the trunk and head and neck regions of adults. Two recurred and one was suspected to have metastasis. All tumors consisted of multiple nodules, in which round or polygonal tumor cells were arranged in sheets or cords within a fibromyxoid background. Characteristic shell-like bone tissues were recognized in all tumors. Based on the grading system proposed by Folpe et al., 2 cases were designated as malignant OFMT and 1 as typical. In addition to S-100 protein, cytokeratin and neuronal markers (neurofilament, CD56 or CD57) were detected in 1 and 2 tumors, respectively. The salient and invariable ultrastructural features included reduplicated basal laminas, which seem to be crucial for the diagnosis.