MDM2 amplification and fusion gene ss18-ssx in a poorly differentiated synovial sarcoma: A rare but puzzling conjunction

Figures

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  Fig. 1. Histological and immunohistochemical features of index case. A–D: poorly differentiated sarcoma displaying a monomorphic spindle-cell proliferation arranged in long fascicles, surrounding adipocytes mostly at the periphery as well as in the centre of the tumor mass. There are stromal changes with collagen bundles and myxoid nests containing histiocytes. Hematoxylin and eosin (H and E) staining (magnification: A: ×50, B: ×100, C: ×200; D:×400). D-E: weak positivity for EMA and AE1-AE3 in the spindle cells (×100). F: diffuse positivity for TLE1 in spindle cells (×100). G, H: MDM2 heterogeneous nuclear positivity in the spindle cell component and no evidence of positivity in the mature adipocytic component (×100). I: CDK4 positivity in 100% of tumor cells (×6). J: HMGA2 expression is positive in spindle cells and negative in adipocytes (×100).

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  Fig. 2. Fluorescence in situ hybridization (FISH) analyses and comparative genomic hybridization on arrays (array-CGH) of index case. A-B: FISH. A: Dual-color probe for MDM2 (green signal) and centromere 12 (red signal) on fixed-paraffin embedded sections showing MDM2 amplification. More than 10 green signals grouped in clusters are observed. B: Break-apart probes for SS18 (green signal: 3′, red signal: 5′) showing one normal SS18 allele (juxtaposed red and green signals) and one rearranged SS18 allele (split red and green signals). C-D: array-CGH. A: Whole genome profile showing the prominent amplification of a large chromosomal segment on chromosome 12q (black arrow). A gain of chromosome 21, a loss of 12q21.3-qter and a loss of chromosome 13 were also detected. D: chromosome 12 profile. Zoom on amplification of 12q13.13-12q21.1: MDM2 log2 ratio Cy3/Cy5 > 1.5. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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  Fig. 3. RNA-sequencing (RNA-Seq) of index case. A: Circos plots illustrating chromosomal translocations SS18-SSX2. Chromosomes are drawn into scale around the rim of the circle and data are plotted on these coordinates. Interchromosomal fusion is indicated by an arc. B: Boxplot presentation based on expression data obtained by Star alignment and count matrices, normalized in Fragments Per Kilobase Million (FPKM), generated using FeatureCount. Relative expression in log2FPKM of CD99, MDM2, MUC1, PS100, SSX2 and SYT are plotted for the index case (G424T07) and a SS+ control group (n = 7). Significant overexpression of MDM2 is highlighted by asterisks.

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  Fig. 4. Clustering analysis of index case. Count matrices, normalized in Fragments Per Kilobase Million (FPKM) data have been used for clustering analysis (Ward method and correlation Pearson with Internal Quantile Range). Well-defined collection of sarcomas was used to assess each specific tumor type or entity (bottom box in x-range), presence of absence of characteristic fusion is represented in the upper box. The index case is figured by a red branch in the dendrogram and yellow box in the light green cluster containing SS samples. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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  Fig. 5. Comparative genomic hybridization on arrays (array-CGH) of case number 87. A: Whole genomic profile showing complex alterations. X-axis coordinates represent chromosomes positions along the genome. Amplifications at 12q13-15, including MDM2 (black arrow) and at 18q11, close to SS18 gene (arrowhead) were observed. B and C: details of chromosomes 12 and 18, respectively.