Inflammatory myofibroblastic tumor (IMT) is a myofibroblastic/fibroblastic neoplasm of intermediate malignant potential. It is frequently characterized by genetic fusion of ALK with a variety of partner genes, which results in the activated ALK signaling pathway that can be targeted with kinase inhibitors. IMTs can occur in the gynecologic tract, with the uterus (corpus and cervix) being the most frequent site. Recent studies suggest that IMTs in the gynecologic tract are underrecognized, and a low-threshold for performing ALK immunohistochemistry has been proposed. The aim of this study was to evaluate the specificity of ALK immunohistochemistry for IMTs among uterine mesenchymal and mixed epithelial/mesenchymal tumors. We performed ALK immunohistochemistry on 14 molecularly confirmed uterine IMTs and 260 other uterine pure mesenchymal and mixed epithelial/mesenchymal tumors. Cases showing any positive cytoplasmic and/or membranous staining of the tumor cells were considered to be ALK positive. All 14 IMTs were confirmed to harbor ALK genetic fusion by RNA sequencing, and ALK immunostaining in the form of granular cytoplasmic positivity with paranuclear accentuation was observed in all 14 cases. ALK was negative (complete absence of staining) in all the other pure mesenchymal tumors and in all mixed epithelial/mesenchymal tumors examined. Our findings show that ALK is a highly specific diagnostic immunohistochemical marker for ALK fusion in uterine mesenchymal tumors. In the work-up of uterine mesenchymal tumors, particularly smooth muscle tumors showing myxoid stromal changes, a diagnosis of IMT should be strongly considered if ALK positivity is observed.

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p53 immunohistochemical analysis of fusion-positive uterine sarcomas Aims: Uterine sarcomas can be grouped into tumours with pathognomonic genetic fusions such as low-grade endometrial stromal sarcoma (LGESS), high-grade endometrial stromal sarcoma (HGESS), and inflammatory myofibroblastic tumour (IMT), and tumours lacking genetic fusions such as leiomyosarcoma (LMS) and undifferentiated uterine sarcoma (UUS). Members of the latter group frequently harbour TP53 mutations. The aim of this study was to evaluate TP53 mutations by the use of immunohistochemistry in fusion-positive uterine sarcomas. Methods and results: We performed p53 immunohistochemical staining on 124 uterine sarcomas harbouring genetic fusions and 38 fusion-negative LMSs and UUSs. These included 41 HGESSs with YWHAE, BCOR and BCORL1 fusions/rearrangements, 13 IMTs with ALK fusion, 12 sarcomas with NTRK1/3 fusion, three sarcomas with PDGFB fusion, and 55 LGESSs with JAZF1, SUZ12 and PHF1 fusions/ rearrangements. All HGESSs, LGESSs, IMTs and sarcomas with PDGFB fusion showed wild-type p53 expression. Among NTRK1/3-positive sarcomas, a TPR-NTRK1-positive sarcoma with nuclear pleomorphism showed mutation-type p53 expression. The remaining 11 NTRK1/3-positive sarcomas showed wild-type p53 expression, except for the subclonal p53 mutation-type staining in a minor pleomorphic focus of an NTRK3-positive sarcoma. Twenty-one of 27 (78%) LMSs and six of nine (67%) UUSs showed mutation-type p53 expression. Conclusion: p53 immunohistochemistry may be considered in the initial work-up of a uterine sarcoma, as mutation-type staining would make a fusion-positive sarcoma very unlikely. Mutation-type p53 expression, however, can be seen in a small subset of NTRK1/3positive sarcomas showing pleomorphic round/ovoid cell histology, which may represent a mechanism of progression in these tumours.

Aims: Dedifferentiated chondrosarcoma (DDCHS) is an aggressive type of chondrosarcoma that results from high-grade transformation of a low-grade chondrosarcoma. Mutations in the isocitrate dehydrogenase (IDH) 1 gene and the IDH2 gene that lead to increased D-2-hydroxyglutarate (2HG) oncometabolite production, promoting tumorigenesis, have been recently described in low-grade cartilaginous neoplasms. The aims of this study were to examine the prevalence of IDH mutations in a single-institution cohort of DDCHS cases and correlate 2HG levels with mutation status. Methods and results: We examined a series of 21 primary DDCHS cases by using Sanger sequencing and quantitative polymerase chain reaction genotyping to look for IDH1/IDH2 mutations, and evaluated the 2HG levels in formalin-fixed paraffin-embedded tumour and matched normal tissue samples by using a fluorometric assay. Seventy-six per cent of DDCHS cases (16/21) harboured a heterozygous IDH1 or IDH2 mutation. Six of 14 IDH-mutated DDCHS cases showed elevated 2HG levels in tumour tissue relative to matched normal tissue. There were no consistent histological or diseasespecific survival differences between IDH-mutated tumours and wild-type tumours. Conclusions: Our study confirms the frequent presence of a variety of IDH1 and IDH2 mutation variants, indicating that a sequencing-based approach is required for DDCHS if IDH is to be used as a diagnostic marker. Similarly to other IDH-mutated tumour types, IDH-mutated DDCHS cases show elevated 2HG levels, indicating that the oncometabolite activity of 2HG may contribute to DDCHS oncogenesis and progression.

PURPOSE This study investigated therapeutic potential of integrated genome and transcriptome profiling of metastatic sarcoma, a rare but extremely heterogeneous group of aggressive mesenchymal malignancies with few systemic therapeutic options. METHODS Forty-three adult patients with advanced or metastatic non-GI stromal tumor sarcomas of various histology subtypes who were enrolled in the Personalized OncoGenomics program at BC Cancer were included in this study. Fresh tumor tissues along with blood samples underwent whole-genome and transcriptome sequencing. RESULTS The most frequent genomic alterations in this cohort are large-scale structural variation and somatic copy number variation. Outlier RNA expression as well as somatic copy number variations, structural variations, and small mutations together suggest the presence of one or more potential therapeutic targets in the majority of patients in our cohort. Point mutations or deletions in known targetable cancer genes are rare; for example, tuberous sclerosis complex 2 provides a rationale for targeting the mammalian target of rapamycin pathway, resulting in a few patients with exceptional clinical benefit from everolimus. In addition, we observed recurrent 17p11-12 amplifications, which seem to be a sarcoma-specific event. This may suggest that this region harbors an oncogene(s) that is significant for sarcoma tumorigenesis. Furthermore, some sarcoma tumors carrying a distinct mutational signature suggestive of homologous recombination deficiency seem to demonstrate sensitivity to double-strand DNA–damaging agents. CONCLUSION Integrated large-scale genomic analysis may provide insights into potential therapeutic targets as well as novel biologic features of metastatic sarcomas that could fuel future experimental and clinical research and help design biomarker-driven basket clinical trials for novel therapeutic strategies.