Yun‐Shao Sung

Approximately 50% of conventional inflammatory myofibroblastic tumors (IMTs) harbor ALK gene rearrangement and overexpress ALK. Recently, gene fusions involving other kinases have been implicated in the pathogenesis of IMT, including ROS1 and in 1 patient PDGFRB. However, it remains uncertain whether the emerging genotypes correlate with clinicopathologic characteristics of IMT. In this study, we expand the molecular investigation of IMT in a large cohort of different clinical presentations and analyze for potential genotype-phenotype associations. Criteria for inclusion in the study were typical morphology and tissue availability for molecular studies. The lack of ALK immunoreactivity was not an excluding factor. As overlapping gene fusions involving actionable kinases are emerging in both IMT and lung cancer, we set out to evaluate abnormalities in ALK, ROS1, PDGFRB, NTRK1, and RET by fluorescence in situ hybridization. In addition, next-generation paired-end RNA sequencing and FusionSeq algorithm was applied in 4 cases, which identified EML4-ALK fusions in 2 cases. Of the 62 IMTs (25 children and 37 adults), 35 (56%) showed ALK gene rearrangement. Of note, EML4-ALK inversion was noted in 7 (20%) cases, seen mainly in the lung and soft tissue of young children including 2 lesions from newborns. There were 6 (10%) ROS1-rearranged IMTs, all except 1 presenting in children, mainly in the lung and intra-abdominally and showed a distinctive fascicular growth of spindle cells with long cell processes, often positive for ROS1 immunohistochemistry. Two of the cases showed TFG-ROS1 fusions. Interestingly, 1 adult IMT revealed a RET gene rearrangement, a previously unreported finding. Our results show that 42/62 (68%) IMTs are characterized by kinase fusions, offering a rationale for targeted therapeutic strategies. Interestingly, 90% of fusion-negative IMTs were seen in adults, whereas >90% of pediatric IMT showed gene rearrangements. EML4-ALK inversion and ROS1 fusions emerge as common fusion abnormalities in IMT, closely recapitulating the pattern seen in lung cancer.

Sclerosing rhabdomyosarcoma (ScRMS) and spindle cell rhabdomyosarcoma (SRMS) have been recently reclassified as a stand-alone pathologic entity, separate from embryonal RMS. Genetically, a subset of the congenital cases display NCOA2 gene rearrangements, whereas tumors occurring in older children or adults harbor MYOD1 gene mutations with or without coexisting PIK3CA mutations. Despite these recent advances, a significant number of tumors lack known genetic alterations. In this study we sought to investigate a large group of pediatric SRMS/ScRMS, spanning a diverse clinical and pathologic spectrum, by using a combined fluorescence in situ hybridization, targeted DNA, and whole-transcriptome sequencing methodology for a more definitive molecular classification. A total of 26 SRMS and ScRMS cases were selected from the 2 participating institutions for the molecular analysis. Ten of the 11 congenital/infantile SRMS showed recurrent fusion genes: with novel VGLL2 rearrangements seen in 7 (63%), including VGLL2-CITED2 fusion in 4 and VGLL2-NCOA2 in 2 cases. Three (27%) cases harbored the previously described NCOA2 gene fusions, including TEAD1-NCOA2 in 2 and SRF-NCOA2 in 1. All fusion-positive congenital/infantile SRMS patients with available long-term follow-up were alive and well, none developing distant metastases. Among the remaining 15 SRMS patients older than 1 year, 10 (67%) showed MYOD1 L122R mutations, most of them following a fatal outcome despite an aggressive multimodality treatment. All 4 cases harboring coexisting MYOD1/PIK3CA mutations shared sclerosing morphology. All 5 fusion/mutation-negative SRMS cases presented as intra-abdominal or paratesticular lesions.

Perivascular epithelioid cell neoplasms (PEComa) are a family of rare mesenchymal tumors with hybrid myo-melanocytic differentiation. Although most PEComas harbor loss-of-function TSC1/TSC2 mutations, a small subset were reported to carry TFE3 gene rearrangements. As no comprehensive genomic study has addressed the molecular classification of PEComa, we sought to investigate by multiple methodologies the incidence and spectrum of genetic abnormalities and their potential genotype-phenotype correlations in a large group of 38 PEComas. The tumors were located in soft tissue (11 cases) and visceral sites (27) including uterus, kidney, liver, lung, and urinary bladder. Combined RNA sequencing and fluorescence in situ hybridization analysis identified 9 (23%) TFE3 gene-rearranged tumors, with 3 cases showing an SFPQ/PSF-TFE3 fusion and 1 case showing a novel DVL2-TFE3 gene fusion. The TFE3-positive lesions showed a distinctive nested/alveolar morphology and were equally distributed between soft tissue and visceral sites. In addition, novel RAD51B gene rearrangements were identified in 3 (8%) uterine PEComas, which showed a complex fusion pattern and were fused to RRAGB/OPHN1 genes in 2 cases. Other nonrecurrent gene fusions, HTR4-ST3GAL1 and RASSF1-PDZRN3, were identified in 2 cases. Targeted exome sequencing using the IMPACT assay was used to address whether the presence of gene fusions is mutually exclusive from TSC gene abnormalities. TSC2 mutations were identified in 80% of the TFE3 fusion-negative cases tested. Coexistent TP53 mutations were identified in 63% of the TSC2-mutated PEComas. Our results showed that TFE3-rearranged PEComas lacked coexisting TSC2 mutations, indicating alternative pathways of tumorigenesis. In summary, this comprehensive genetic analysis significantly expands our understanding of molecular alterations in PEComas and brings forth the genetic heterogeneity of these tumors.

Round cell sarcomas harboring CIC-DUX4 fusions have recently been described as highly aggressive soft tissue tumors of children and young adults. Due to partial morphologic and immunohistochemical overlap with Ewing sarcoma (ES), CIC-DUX4-positive tumors have generally been classified as ES-like and managed similarly; however, a systematic comparison at the molecular and immunohistochemical levels between these two groups has not yet been conducted. Based on an initial observation that CIC-DUX4-positive tumors show nuclear immunoreactivity for WT1 and ETS transcription factors, FLI1 and ERG, we performed a detailed immunohistochemical and molecular analysis including these markers, to further investigate the relationship between CIC-DUX4 tumors and ES. The study group included 21 CIC-DUX4-positive sarcomas and 20 EWSR1-rearranged ES. Immunohistochemically, CIC-DUX4 sarcomas showed membranous CD99 positivity in 18 (86%) cases, but only 5 (24%) with a diffuse pattern, while WT1 and FLI1 were strongly positive in all cases. ERG was positive in 18% of cases. All ES expressed CD99 and FLI1, while ERG positivity was only seen in EWSR1-ERG fusion positive ES. WT1 was negative in all ES. Expression profiling validated by q-PCR revealed a distinct gene signature associated with CIC-DUX4 fusion, with upregulation of ETS transcription factors (ETV4, ETV1, and ETV5) and WT1, among top overexpressed genes compared to ES, other sarcomas and normal tissue. In conclusion, the distinct gene signature and immunoprofile of CIC-DUX4 sarcomas suggest a distinct pathogenesis from ES. The consistent WT1 expression may provide a useful clue in the diagnosis in the context of round cell sarcomas negative for EWSR1 rearrangement. © 2014 Wiley Periodicals, Inc.

Tumors characterized by co-expression of S100 and CD34, in the absence of SOX10, remain difficult to classify. Triggered by a few index cases with monomorphic cytomorphology and distinctive stromal and perivascular hyalinization, immunopositivity for S100 and CD34, and RAF1 and NTRK1 fusions, the authors undertook a systematic review of tumors with similar features. Most of the cases selected were previously diagnosed as low-grade malignant peripheral nerve sheath tumors, while others were deemed unclassified. The tumors were studied with targeted RNA sequencing and/or FISH. A total of 25 cases (15 adults and 10 children) with kinase fusions were identified, including 8 cases involving RAF1, 2 BRAF, 14 NTRK1, and 1 NTRK2 gene rearrangements. Most tumors showed a monomorphic spindle cell proliferation with stromal and perivascular keloidal collagen, in a patternless architecture, with only occasional scattered pleomorphic or multinucleated cells. Most cases showed low cellularity, a low mitotic count, and absence of necrosis. Although a subset showed overlap with lipofibromatosis-like neural tumors, the study group showed distinctive hyalinization and overt malignant features, such as highly cellular fascicular growth and primitive appearance. All tumors showed co-expression of S100 and CD34, ranging from focal to diffuse. SOX10 was negative in all cases. NTRK1 immunohistochemistry showed high levels of expression in all tumors with NTRK1 gene rearrangements. H3K27me3 expression performed in a subset of cases was retained. These findings together with the recurrent gene fusions in RAF1, BRAF, and NTRK1/2 kinases suggest a distinct molecular tumor subtype with consistent S100 and CD34 immunoreactivity.