Abstract PR16: Multiplatform analysis of paired primary and recurrent well- and dedifferentiated liposarcoma samples defines copy number alterations as dominant drivers of initiation and progression

Objective: Initiation of well-differentiated (WD) and dedifferentiated (DD) liposarcoma is driven by 12q13-15 amplification and consequent MDM2 and CDK4 overexpression, but mechanisms that regulate the variable biologic behavior of WD/DD tumors remain poorly understood. We used a multiplatform analysis of paired WD and DD samples to identify genomic events with potential to contribute to liposarcomagenesis. Methods: From serial tumor resections performed on the same patient, we collected paired WD/DD (n=7) or WD/WD (n=2) test samples and normal tissue. Samples were analyzed using whole-exome sequencing, array comparative genomic hybridization (aCGH), Solexa small RNA sequencing, and, in a subset, RNA-seq. Findings were validated in WD/DD cohorts analyzed by custom capture array (n=201), aCGH (n=210), Affymetrix U133A microarrays (n=146), and Solexa (n=118). Lentivirus was used to deliver shRNA to WD cells in vitro; proliferation was assayed by CyQuant, differentiation by immunoblot/oil red O staining, and gene expression by Illumina microarrays. Results: 12q13-15 amplification was observed in all WD/DD test and validation samples. Among WD samples, 1q21-24 and 6q23-25 amplifications were found in test samples and in 28% and 18% of the validation set, respectively. Of genes upregulated in WD vs. normal fat test samples, 465 were validated in the larger cohort [≥2-fold change (FC), FDR MDM2 or drug inhibition of CDK4 in vitro negatively regulated 11% of the genes, including AURKA and its regulators TPX2 and KIF11 . 6q23-25 amplification was associated with local recurrence (LR) after primary WD resection (HR 10.9, p CCDC28A and TAB2 , an AP-1 regulator (1.7- and 1.9-FC, FDRs TAB2 inhibition reduced proliferation by >90%. Comparison of matched WD/DD samples showed retained amplification of 12q13-15 and 6q23-25 after progression. In contrast to WD, DD showed strong association of the 6q23-25 CNA with increased expression of 6q genes TCF21 and HBS1L (16- and 4-FC, FDRs TAB2 or CCDC28A , suggesting that additional progression events alter the oncogenic effects of initiation-associated CNAs in DD vs WD. Direct comparison of paired DD/WD test samples revealed recurrent 13q loss arising during dedifferentiation (n=3). 13q loss was found in 28% of the DD validation set and associated with reduced expression of 13q genes MYCBP2 and IRS2 , regulators of insulin signaling. shRNA inhibition of MYCBP2 or IRS2 in vitro had little effect on WD differentiation, but inhibition of both genes decreased levels of PPARG, FABP4, PLIN and oil red O staining (70% reduction). Uncommon mutations in genes regulating steroid-hormone activation (e.g., NCOA6 , KMT2C ), adaptive immunity (e.g., LILRA1 , NFKB1 ), and RTK signaling (e.g., NRG1 , FGFR1 ) were identified in 11%, 6%, and 11% of WD/DD samples, respectively, but did not associate with differentiation. Conclusions: Genes upregulated during WD initiation are commonly located in regions of CNA or regulated by 12q23-25 oncogenes MDM2 and CDK4 (e.g., AURKA , a potential therapeutic target). 6q23-26 amplification, observed in subsets of both WD and DD, associates with LR of WD, but expression of 6q23-26 genes with potential to modulate oncogenesis (e.g., TAB2 vs TCF21 ) differs in WD and DD tumors, suggesting that the CNA may differentially modulate early and late disease. Losses affecting broad chromosome regions such as 13q likely mediate progression by affecting multiple regulators of adipogenesis pathways (e.g., insulin signaling), while mutations have little effect on dedifferentiation. Citation Format: Aimee M. Crago, Nicholas D. Socci, Li-Xuan Qin, Fatima Wilder, Rachael O9Connor, Amanda Craig, Willem van Houdt, Nils Weinhold, Cyriac Kandoth, Agnes Viale, Cristina Antonescu, Sam Singer. Multiplatform analysis of paired primary and recurrent well- and dedifferentiated liposarcoma samples defines copy number alterations as dominant drivers of initiation and progression [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr PR16.