Abstract 2163: Molecular characteristics of CDK4 and/or MDM2 amplification in Chinese soft tissue sarcoma (STS) patients
Authors: Jin Gu , Wang Chunyang , Wang Xiaojuan , He Qifan , Ma Tonghui 
Published: July 2021

Abstract
Background: Cyclin-dependent kinase 4 (CDK4) and mouse double minute 2 homolog (MDM2) amplification occur at high frequency in well-differentiated liposarcoma and dedifferentiated liposarcoma, which are generally considered to be diagnostic criteria for these tumors. Studies have also reported that CDK4 and/or MDM2 amplification can emerge in STS subtypes, such as Ewing's sarcoma (ES) and fibrosarcoma (FS). However, the clinical pathological and molecular characteristics of CDK4 and/or MDM2 amplification in STS are still unclear. We systematically depicted the clinical characteristics of MDM2 and CDK4 gene amplification in Chinese STS patients (pts), aiming to assist the precise diagnosis and treatment of STS.
Methods: Totally 184 Chinese pts with different STS subtypes were included in this study. In terms of subtypes distribution, the cohort contained multiple STS subtypes including myofibroblastic sarcoma (MFS, n = 23), liposarcoma (LPS, n = 21), FS (n = 20), rhabdomyosarcoma (RMS, n = 19), liomyosarcoma (LMS, n = 12), undifferentiated pleomorphic sarcoma (n = 11), clear cell sarcoma (n = 10), synovial sarcoma (n = 8), ES (n = 7), hemangiosarcoma (n=7), other rare subtypes (n = 37) and unknown types (n = 9). The amplification status of CDK4 and MDM2 in the tumor tissues of these pts was reviewed by the DNA and RNA next generation sequencing method.
Results: Totally 16.8% (31/184) of the Chinese STS pts harbored CDK4 and/or MDM2 amplification. Among the 31 pts, 17 were with co-amplification of CDK4 and MDM2, including 12 LPSs, two RMSs, one MFS, one LMS and one FS. Fourteen pts were with single amplification of MDM2 or CDK4, including LPS (n = 4), RMS (n = 3), MFS (n = 3), FS (n = 2), ES (n = 1), and malignant peripheral nerve sheath tumor (n = 1). In LPS, the ratios of co-amplification and single amplification of CDK4/MDM2 were 57.1% (12/21) and 19.0% (4/21) respectively. Other STS subtypes with high frequency of CDK4 and/or MDM2 amplification included RMS (26.3%, 5/19) and MFS (19.4%, 4/23). Meanwhile, our study revealed that co-amplification of CDK4 and MDM2 appeared to be a strong driver event in STS, which mutated exclusively with other driver genes, such as TP53, MYOD1, ATRX and PTEN. Pts with co-amplification of CDK4 and MDM2 were likely to benefit from the treatment of CDK4 and/or MDM2 inhibitors. However, more than half of the pts with single amplification of CDK4 or MDM2 were accompanied by mutations in other driven genes, such as FLI1-EWSR1 fusion, PAX3-FOXO1 fusion, MYOD1 p.L122R, TP53 p.R273S, and NRAS p.G13C. In these pts, single amplification of CDK4 or MDM2 may not be the main driver event, who may be less likely to benefit from CDK4 or MDM2 inhibitor monotherapy.
Conclusion: Our study revealed the clinicopathologic and molecular features of CDK4 and/or MDM2 amplification in Chinese STS pts, which can guide the selection of personalized treatment strategies in STS pts.
Citation Format: Gu Jin, Chunyang Wang, Xiaojuan Wang, Qifan He, Tonghui Ma. Molecular characteristics of CDK4 and/or MDM2 amplification in Chinese soft tissue sarcoma (STS) patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2163.