Murine Double Minute 2 Amplification Research Articles

A structure-based virtual screening identifies a novel MDM2 antagonist in the activation of the p53 signaling and inhibition of tumor growth.

p53, a tumor suppressor protein, has a vital role in the regulation of the cell cycle, apoptosis, and DNA damage repair. The degradation of p53 is predominantly controlled by the murine double minute 2 (MDM2) protein, a ubiquitin E3 ligase. The overexpression or amplification of MDM2 is commonly observed in various human cancers bearing wild-type p53 alleles, leading to the rapid degradation of the p53 protein and the attenuation of p53 tumor suppression functions. Thus, a major effort in p53-based cancer therapy has been to research MDM2 antagonists that specifically stabilize and activate p53, leading to the suppression of tumor growth. However, despite numerous efforts to develop MDM2 antagonists, to date they have failed to reach clinical use, largely because of the cytotoxicity associated with these small molecules. This study used our newly designed structure-based virtual screening approach on a commercial compound library to identify a novel compound, CGMA-Q18, which directly binds to MDM2, leading to the activation of p53, the induction of apoptosis, and cell cycle arrest in cancer cells. Notably, CGMA-Q18 significantly inhibited tumor xenograft growth in nude mice without observable toxicity. These findings highlight our useful virtual screening protocol and CGMA-Q18 as a putative MDM2 antagonist.

Abstract CT066: Phase 1 study of MDM2 antagonist ASTX295 in patients with solid tumors with wild-type TP53

Abstract Background: ASTX295 is a novel small molecule antagonist of human Murine Double Minute 2 (MDM2), which tightly regulates the level and activity of the p53 tumor suppressor. To minimize potential thrombocytopenia previously seen with antagonism of this target, ASTX295 was designed to have a short half-life (t1/2) with decreased bone marrow (BM) exposure. ASTX295 has proapoptotic and tumor growth inhibitory activity in preclinical cancer (CA) models. We report here the safety and preliminary efficacy of the phase 1 and dose expansion portions of Study ASTX295-01. Methods: ASTX295-01 is a first-in-human, open-label, multicenter, phase 1/2 study to assess safety, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary clinical activity of ASTX295 (NCT03975387). Eligible patients (advanced solid tumors with Wild-Type [WT] TP53, ECOG PS 0-2, adequate organ and bone marrow function, etc.) had oral administration of ASTX295 starting at a daily dose of 15 mg. Dose escalation was by standard 3 + 3 with cohorts testing multiple regimens. Safety was assessed by CTCAE and disease was assessed by RECIST 1.1. Safety and efficacy and dosing recommendations were overseen by the Data Safety Review Committee. Results:83 subjects were enrolled in over 14 cohorts, evaluating daily (QD) and intermittent dosing regimens and the effect of food. The mean age of subjects on study was 60.1 year, 56.9 were male, with 2.94 (0-15) prior chemotherapy regimens. For PK exposure, the total weekly AUC for 400 mg QD and 660 twice a week (BIW) are similar. The median tmax is 3 hours and mean t1/2 is 4-6 hours. PD demonstrates p53 pathway modulation. Nausea, vomiting, diarrhea, and fatigue were dose limiting. RP2D regimens were 660 mg BIW and 400 mg QD and these regimens were expanded with a total of 25 additional subjects. The most common treatment related AEs for both regimens were nausea, diarrhea, and vomiting at 76.2%,76.2%, and 33.3% respectively, for daily and 71.4%, 47.6%, and 33.3%, for intermittent. Grade 3 GI AEs were reported in 14.3% of subjects in the daily cohort vs 9.5% in the intermittent; none had Grade ≥ 4. One subject had grade 2 thrombocytopenia. Based on decreased incidence and duration of GI AEs, 660 mg BIW was selected as the RP2D.Multiple objective responses were seen, including 1 subject with non-small cell lung CA and 3 subjects with liposarcoma (LPS), a tumor with frequent MDM2 amplification. For LPS the ORR is 7.9% (de-differentiated 7.7%, well differentiated 8.0%), with a PFS of 7.95 and 9.66 months respectively, along with a 16-week disease control rate of 69.2% and 72.0%. Five subjects with GBM were enrolled, 4 with MDM2 amplification, 3 of whom showed evidence of tumor regression, with one subject remaining on study for > 34 cycles. Conclusion:ASTX295 was well tolerated at doses producing p53 pathway modulation with manageable toxicities, notably avoiding significant thrombocytopenia. Preliminary single agent efficacy was observed in heavily pretreated subjects across multiple solid tumor types with WT TP53. Citation Format: Ecaterina E. Dumbrava, Fabio M. Iwamoto, Mark Agulnik, Mohammed Milhem, Anthony W. Tolcher, Rashmi Chugh, Michael J. Demeure, Alain Mita, Kurt Demel, Mark Diamond, Beloo Mirakhur, Laksmi Wilson, Aram Oganesian, Danna Chan, Harold N. Keer, Jason Taylor, Martin J. Sims, Andrea Biondo, Simone Jueliger, Alexander Spira. Phase 1 study of MDM2 antagonist ASTX295 in patients with solid tumors with wild-type TP53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT066.

Abstract P6-10-10: Genetic alterations in breast cancer associated with MDM2 dependency and sensitivity to the MDM2 inhibitor milademetan

Abstract Background: Murine double minute 2 (MDM2), a potent negative regulator of p53, promotes tumorigenesis if dysregulated. MDM2 dysregulation occurs via different mechanisms, including MDM2 gene amplification, MDM2 overexpression, and loss of cyclin-dependent kinase inhibitor 2A (CDKN2A), which encodes the MDM2 regulator p14ARF. Combined inactivation of MDM2 and GATA3 in hormone receptor-positive (HR+) breast cancer is lethal to the cell. Pharmacologic inhibition of MDM2 is a rational therapeutic strategy for MDM2-dependent, TP53 wildtype (WT) tumors, including tumors with MDM2 amplification or CDKN2A loss, and GATA3-mutant HR+ breast cancers. We determined the frequency and associated characteristics of genetic alterations of MDM2-dependent breast cancers, and evaluated sensitivity of these tumors to the small-molecule MDM2 inhibitor milademetan (RAIN-32). Methods: Genomic data were obtained from three datasets: METABRIC; TCGA PanCancer Atlas, GDC v23.0 (April 2020); AACR Genie, v11. Among TP53 WT breast cancer samples from each dataset, the frequency of GATA3 frameshift mutations, MDM2 amplification (copy number [CN] ≥12), and CDKN2A homozygous loss was determined individually and as co-alterations. The antitumoral activity of milademetan was evaluated in a GATA3-mutant, TP53 WT HR+ breast cancer cell line (MCF7 GATA3 G336fs*17), a breast xenograft model (MCF7 GATA3 G335fs), and ex vivo in MDM2-amplified patient-derived breast cancer organoids (CTG-2810, ER+/PR+/HER2–, MDM2 CN 8). Results: Genetic alteration frequencies in TP53 WT breast cancers by dataset are shown in the Table. GATA3 frameshift mutations (7.3–11.7%), MDM2 amplification (0.3–1.1%), and CDKN2A loss (0.2–1.2%) occurred across breast tumors, but were found with highest frequencies in HR+ tumors. Co-alteration frequencies in TP53 WT breast cancers across the aforementioned datasets were < 1%: GATA3 mutations/MDM2 CN ≥12 (0.2–0.3%); GATA3 mutations/CDKN2A loss (0.1–0.2%); MDM2 CN ≥12/CDKN2A loss (0%). Mean MDM2 expression (log2 (TPM+1)) in HR+ breast cancers (TCGA) were: GATA3 mutations, 5.12; CDKN2A loss, 5.88; MDM2 CN ≥12, 8.13, TP53 WT without these alterations, 4.78; mutant TP53, 4.35. A GATA3-mutant ER+ breast cancer cell line was sensitive to milademetan in vitro (IC50 126 nM). Milademetan 100 mg/kg displayed antitumor activity in GATA3-mutant HR+ breast xenograft and PDX models (p< 0.05 vs. vehicle). Milademetan also displayed activity in MDM2-amplified HR+ breast cancer organoids (IC50 0.2 μM). In a phase I study (NCT01877382), a patient with heavily pretreated MDM2-amplified breast cancer (MDM2 CN 16.8) had tumor shrinkage (18.2%) and PFS of 7.3 months with milademetan (orally 260 mg 3/14 days). Conclusions: The frequency of genetic alterations potentially targetable by MDM2 inhibition among TP53 WT breast cancers (i.e., GATA3 mutations, MDM2 amplification, and CDKN2A loss) is greatest in the HR+ subset, and these genetic biomarkers are associated with higher MDM2 expression. Preclinical data show that the MDM2 inhibitor milademetan has antitumor activity in GATA3-mutant and MDM2-amplified HR+ breast cancers, and support the clinical evaluation of milademetan in these tumors. Two clinical trials of milademetan – MANTRA-2 (Phase 2 basket study in solid tumors with TP53 WT and MDM2 CN ≥12; NCT05012397) and MANTRA-4 (Phase 1 study of milademetan + atezolizumab in solid tumors with CDKN2A loss) – are enrolling patients or in planning. Table. Citation Format: Francois-Clement Bidard, Diana Bello Roufai, Arielle J. Medford, Vijaya Tirunagaru, Robert C. Doebele, Aditya Bardia. Genetic alterations in breast cancer associated with MDM2 dependency and sensitivity to the MDM2 inhibitor milademetan [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-10.

MDM2 gene a mplification in s kin c ancer p atients

Skin cancer: Skin cancer is the uncontrolled proliferation of abnormal skin cells; skin cancer is classified into non-melanoma (squamous cell carcinoma and basal cell carcinoma) and melanoma. Approximately, 90% of skin cancers are caused by ultraviolet radiation, because of ultraviolet radiation emits to damage of skin cells DNA resulting in genetic mutations and formation of skin cancer.
 Materials and methods: This study evaluated paraffin blocks from 17 specimen randomly selected from patients with skin cancer, and 6 specimens from patients non cancer patients as control group for comparison .This study was carried out in Laboratories of College of Science, Wasit University and AL Zahraa and ALKarama Teaching Hospitals, from October 2014 to April 2015. In this study MDM2( murine double minute 2) gene amplification was assessed by chromogenic in situ hybridization (CISH) technique.
 Results: This study showed that there was no significant difference between skin cancer patients and control group in relation to MDM2 amplification (p>0.05), but presence of highly significant difference between patients of skin cancer and control group in relation to amplification intensity of MDM2 (p<0.05). Moreover, and according to histological type, our finding found significant difference between the types of skin cancer in relation to MDM2 amplification (p<0.05). Additionally, there were significant differences between patients of basal cell carcinoma and squamous cell carcinoma and control group in relation to MDM2 amplification(p<0.05).
 Conclusion: We conclude that MDM2 amplification was high in types of skin cancer (BCC and SCC) because of MDM2 amplification in keratocytes of the epidermis may be associated with entry of these cells into the differentiation program.

Abstract CT123: A phase 2 study of the MDM2 inhibitor milademetan in patients with TP53-wild type and MDM2-amplified advanced or metastatic solid tumors (MANTRA-2)

Abstract Background: Murine double minute 2 (MDM2) is a potent negative regulator of the tumor suppressor p53. MDM2 induces degradation of p53 and promotes tumorigenesis in solid tumors, and preclinical models have shown that inhibition of MDM2 can restore p53 tumor suppressor activity in TP53-wild type (WT), MDM2-amplified tumors. We performed a mutual exclusivity analysis of patients with solid tumors (n=42,125; AACR Project GENIE) and found that the frequency of co-occurring TP53 mutations decreased with increasing MDM2 copy number. An MDM2 copy number of 12 was chosen as the threshold. An estimated 1.1% of solid tumors meet this molecular criteria, excluding glioblastomas, de-differentiated liposarcomas, and intimal sarcomas where this signature is enriched. Milademetan (RAIN-32), an oral, selective MDM2 inhibitor, inhibits growth of TP53-WT/MDM2-amplified cell lines and patient-derived xenograft models from varying tumor types. Furthermore, tumor regression was observed in 3/3 non-liposarcoma patients with MDM2 copy number >12 in a phase 1 trial of milademetan. MANTRA-2 (RAIN-3202) is a phase 2, multicenter, single-arm, open-label, basket trial designed to evaluate the efficacy or clinical benefit of milademetan in TP53-WT solid tumors with MDM2 amplification (copy number ≥12). Methods: Eligible patients must be ≥18 years of age with histologically and/or cytologically confirmed locally advanced, incurable or metastatic solid tumors refractory to standard therapy. Local testing demonstrating TP53 WT and MDM2 amplification is required, defined as a MDM2 copy number ≥12 or 6-fold increase. Patients with well-differentiated/de-differentiated liposarcomas, intimal sarcomas, or primary central nervous system tumors are excluded. Prior treatment with an MDM2 inhibitor is not permitted. Patients receive milademetan 260 mg orally once daily on Days 1-3 and 15-17 of a 28-day cycle. Tumor response is evaluated by RECIST v1.1 at Weeks 8, 16, 24, and 32, and then every 12 weeks. Primary endpoint: objective response rate. Secondary endpoints include: duration of response; progression-free survival; growth modulation index; disease control rate; overall survival; safety; health-related quality of life scores. Exploratory endpoints include: biomarkers in blood and/or tumor tissue; pharmacodynamics; pharmacokinetics. Enrollment of 65 patients is planned to ensure that 57 patients have centrally confirmed TP53 WT and MDM2 copy number ≥12. The trial opened in November 2021 and is actively enrolling patients. ClinicalTrials.gov: NCT05012397. Citation Format: Ecaterina I. Dumbrava, Glenn J. Hanna, Gregory M. Cote, Thomas E. Stinchcombe, Melissa L. Johnson, Christopher T. Chen, Siddhartha H. Devarakonda, Naisargee Shah, Feng Xu, Robert C. Doebele, Mrinal M. Gounder. A phase 2 study of the MDM2 inhibitor milademetan in patients with TP53-wild type and MDM2-amplified advanced or metastatic solid tumors (MANTRA-2) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT123.

Abstract CT235: MANTRA: A randomized, multicenter, phase 3 study of the MDM2 inhibitor milademetan versus trabectedin in patients with de-differentiated liposarcomas

Abstract Background: Murine double minute 2 (MDM2) is a negative regulator of tumor suppressor protein p53. MDM2 induces degradation of p53 and promotes tumorigenesis. MDM2 amplification occurs in many cancers but is documented in up to 100% of well-differentiated or de-differentiated liposarcomas (WD/DDLPS) [Cancer Genome Atlas Research Network. Cell 2017]. Inhibition of the MDM2-p53 interaction is a promising therapeutic approach to restore p53 tumor suppressor activity in WD/DDLPS. Milademetan (RAIN-32) is a small-molecule MDM2 inhibitor that inhibits the MDM2-p53 interaction and restores p53 function at nanomolar concentrations. In a phase 1 study, milademetan showed promising efficacy in 53 patients with WD/DDLPS when administered on an intermittent schedule (260 mg QD on Days 1-3 and 15-17 on a 28-day cycle), with a median progression-free survival (PFS) of 7.4 months [Gounder et al. AACR-NCI-EORTC 2020]. WD/DDLS are relatively resistant to chemotherapy, and systemic treatment options for patients with advanced disease are limited. MANTRA (RAIN-3201) is a randomized, multicenter, open-label, phase 3 registration study designed to evaluate the efficacy and safety of milademetan versus trabectedin in patients with unresectable or metastatic DDLPS with disease progression on ≥1 prior systemic therapies. Methods: Eligible patients are ≥18 years of age with histologically confirmed unresectable and/or metastatic DDLPS, with or without a WD component, who have received ≥1 prior systemic therapies, including ≥1 anthracycline-based regimen, with radiographic evidence of progression by RECIST v1.1 within 6 months before study entry. Prior treatment with trabectedin or an MDM2 inhibitor is not permitted. Patients will be randomly assigned (1:1) to receive milademetan (260 mg once daily orally Days 1-3 and 15-17 on a 28-day cycle) or trabectedin (1.5 mg/m2 as a 24-hour intravenous infusion every 3 weeks). Randomization is stratified by Eastern Cooperative Oncology Group performance status (0 or 1) and number of prior treatments for WD/DDLPS (≤2 or >2). Tumor response will be evaluated by RECIST v1.1 at Weeks 8, 16, 24, and 32, and then every 12 weeks. Primary endpoint: PFS by blinded independent central review. Secondary endpoints: overall survival; disease control rate; objective response rate; duration of response; PFS by investigator assessment; safety; health-related quality of life. Exploratory endpoints: molecular markers in peripheral blood and/or tumor tissue; milademetan pharmacokinetics. To demonstrate a 3-month increase in PFS (from 3 to 6 months) corresponding to a hazard ratio of 0.5, approximately 160 patients will be required to observe 105 events with 93.9% power and 2-sided significance level of 5%. ClinicalTrials.gov: NCT04979442. Citation Format: Mrinal M. Gounder, Gary K. Schwartz, Robin L. Jones, Sant P. Chawla, Victoria S. Chua-Alcala, Silvia Stacchiotti, Andrew J. Wagner, Gregory M. Cote, Robert G. Maki, Hanna Kosela-Paterczyk, Dale R. Shepard, Naisargee Shah, Richard Bryce, Robert C. Doebele, Shreyaskumar Patel. MANTRA: A randomized, multicenter, phase 3 study of the MDM2 inhibitor milademetan versus trabectedin in patients with de-differentiated liposarcomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT235.

A phase 2 study of the MDM2 inhibitor milademetan in patients with TP53-wild type and MDM2-amplified advanced or metastatic solid tumors (MANTRA-2).

TPS3165 Background: Murine double minute 2 (MDM2) is a potent negative regulator of the tumor suppressor p53. MDM2 induces degradation of p53 and promotes tumorigenesis in solid tumors, and preclinical models have shown that inhibition of MDM2 can restore p53 tumor suppressor activity in TP53-wild type (WT), MDM2-amplified tumors. We performed a mutual exclusivity analysis of patients with solid tumors (n = 42,125; AACR Project GENIE) and found that the frequency of co-occurring TP53 mutations decreased with increasing MDM2 copy number. An MDM2 copy number of 12 was chosen as the threshold. An estimated 1.1% of solid tumors meet this molecular criteria, excluding glioblastomas, dedifferentiated liposarcomas, and intimal sarcomas where this signature is enriched. Milademetan (RAIN-32), an oral, selective MDM2 inhibitor, inhibits growth of TP53-WT/ MDM2-amplified cell lines and patient-derived xenograft models from varying tumor types. Furthermore, tumor regression was observed in 3/3 non-liposarcoma patients with MDM2 copy number > 12 in a phase 1 trial of milademetan. MANTRA-2 (RAIN-3202) is a phase 2, multicenter, single-arm, open-label, basket trial designed to evaluate the efficacy or clinical benefit of milademetan in TP53-WT solid tumors with MDM2 amplification (copy number ≥ 12). Methods: Eligible patients must be ≥ 18 years of age with histologically and/or cytologically confirmed locally advanced, incurable or metastatic solid tumors refractory to standard therapy. Local testing demonstrating TP53 WT and MDM2 amplification is required, defined as a MDM2 copy number ≥ 12 or 6-fold increase. Patients with well-differentiated/de-differentiated liposarcomas, intimal sarcomas, or primary central nervous system tumors are excluded. Prior treatment with an MDM2 inhibitor is not permitted. Patients receive milademetan 260 mg orally once daily on Days 1–3 and 15–17 of a 28-day cycle. Tumor response is evaluated by RECIST v1.1 at Weeks 8, 16, 24, and 32, and then every 12 weeks. Primary endpoint: objective response rate. Secondary endpoints include: duration of response; progression-free survival; growth modulation index; disease control rate; overall survival; safety; health-related quality of life scores. Exploratory endpoints include: biomarkers in blood and/or tumor tissue; pharmacodynamics; pharmacokinetics. Enrollment of 65 patients is planned to ensure that 57 patients have centrally confirmed TP53 WT and MDM2 copy number ≥ 12. The trial opened in November 2021 and is actively enrolling patients. Clinical trial information: NCT05012397.

MANTRA: A randomized, multicenter, phase 3 study of the MDM2 inhibitor milademetan versus trabectedin in patients with de-differentiated liposarcomas.

TPS11589 Background: Murine double minute 2 (MDM2) is a negative regulator of tumor suppressor protein p53. MDM2 induces degradation of p53 and promotes tumorigenesis. MDM2 amplification occurs in many cancers but is documented in up to 100% of well-differentiated or dedifferentiated liposarcomas (WD/DDLPS) [Cancer Genome Atlas Research Network. Cell 2017]. Inhibition of the MDM2-p53 interaction is a promising therapeutic approach to restore p53 tumor suppressor activity in WD/DDLPS. Milademetan (RAIN-32) is a small-molecule MDM2 inhibitor that inhibits the MDM2-p53 interaction and restores p53 function at nanomolar concentrations. In a phase 1 study, milademetan showed promising efficacy in 53 patients with WD/DDLPS when administered on an intermittent schedule (260 mg QD on Days 1–3 and 15–17 on a 28-day cycle), with a median progression-free survival (PFS) of 7.4 months [Gounder et al. AACR-NCI-EORTC 2020]. WD/DDLS are relatively resistant to chemotherapy, and systemic treatment options for patients with advanced disease are limited. MANTRA (RAIN-3201) is a randomized, multicenter, open-label, phase 3 registration study designed to evaluate the efficacy and safety of milademetan versus trabectedin in patients with unresectable or metastatic DDLPS with disease progression on ≥ 1 prior systemic therapies. Methods: Eligible patients are ≥ 18 years of age with histologically confirmed unresectable and/or metastatic DDLPS, with or without a WD component, who have received ≥ 1 prior systemic therapies, including ≥ 1 anthracycline-based regimen, with radiographic evidence of progression by RECIST v1.1 within 6 months before study entry. Prior treatment with trabectedin or an MDM2 inhibitor is not permitted. Patients will be randomly assigned (1:1) to receive milademetan (260 mg once daily orally Days 1–3 and 15–17 on a 28-day cycle) or trabectedin (1.5 mg/m2 as a 24-hour intravenous infusion every 3 weeks). Randomization is stratified by Eastern Cooperative Oncology Group performance status (0 or 1) and number of prior treatments for WD/DDLPS (≤ 2 or > 2). Tumor response will be evaluated by RECIST v1.1 at Weeks 8, 16, 24, and 32, and then every 12 weeks. Primary endpoint: PFS by blinded independent central review. Secondary endpoints: overall survival; disease control rate; objective response rate; duration of response; PFS by investigator assessment; safety; health-related quality of life. Exploratory endpoints: molecular markers in peripheral blood and/or tumor tissue; milademetan pharmacokinetics. To demonstrate a 3-month increase in PFS (from 3 to 6 months) corresponding to a hazard ratio of 0.5, approximately 160 patients will be required to observe 105 events with 93.9% power and 2-sided significance level of 5%. Clinical trial information: NCT04979442.

Abstract P031: MANTRA: A randomized, multicenter, phase 3 study of the MDM2 inhibitor milademetan (RAIN-32) versus trabectedin in patients with de-differentiated liposarcoma

Abstract Background: p53 plays a central role in tumor suppression and maintenance of genome integrity. Murine double minute 2 (MDM2) is a ubiquitin ligase that inhibits p53 transcriptional activity and induces p53 degradation through ubiquitination. MDM2 amplification occurs in many cancers but is universal in well-differentiated (WD) or de-differentiated (DD) liposarcomas (100% of cases) [Cancer Genome Atlas Research Network. Cell 2017]. Current therapies for WD/DD liposarcomas include anthracycline-based chemotherapy, eribulin, and trabectedin. Inhibition of the MDM2-p53 interaction is a promising therapeutic approach to restore p53 tumor suppressor activity in liposarcomas. Milademetan (RAIN-32) is a small-molecule MDM2 inhibitor that inhibits the MDM2-p53 interaction and restores p53 function at nanomolar concentrations. In a phase 1 study, milademetan showed promising efficacy in patients with WD/DD liposarcoma when administered on an intermittent schedule (260 mg on Days 1–3 and 15–17 every 28 days), with a median progression-free survival (PFS) of 7.4 months [Gounder et al. AACR-NCI-EORTC 2020]. MANTRA (RAIN-3201) is a randomized, multicenter, open-label, phase 3 registration study designed to evaluate the efficacy and safety of milademetan versus trabectedin in patients with unresectable or metastatic DD liposarcoma with disease progression on ≥1 prior systemic therapies, including ≥1 anthracycline-based regimen (EudraCT: 2021-001394-23). Methods: Eligible patients are ≥18 years of age with histologically confirmed unresectable and/or metastatic DD liposarcoma, with or without a WD component, who have received ≥1 prior systemic therapies, including ≥1 anthracycline-based regimen, with radiographic evidence of progression within 6 months before study entry. Prior treatment with trabectedin or an MDM2 inhibitor is not permitted. Patients will be randomly assigned (1:1) to receive milademetan (260 mg once daily orally Days 1–3 and 15–17 on a 28-day cycle) or trabectedin (1.5 mg/m2 as a 24-hour intravenous infusion every 3 weeks). Randomization is stratified by Eastern Cooperative Oncology Group performance status (0 or 1) and number of prior treatments for liposarcoma (≤2 or >2). Tumor response will be evaluated by RECIST v1.1 at Weeks 8, 16, 24, and 32, and then every 12 weeks. Primary endpoint: PFS by blinded independent central review. Secondary endpoints: overall survival; disease control rate; objective response rate; duration of response; PFS by investigator assessment; safety; health-related quality of life. Exploratory endpoints: molecular markers in peripheral blood and/or tumor tissue; milademetan pharmacokinetics. To demonstrate a 3-month increase in PFS (from 3 to 6 months) corresponding to a hazard ratio of 0.5, approximately 160 patients will be required to observe 105 events with 93.9% power and 2-sided significance level of 5%. MANTRA is currently open to enrollment. Citation Format: Mrinal Gounder, Gary Schwartz, Robin Jones, Shreyaskumar Patel, Silvia Stacchiotti, Andrew Wagner, Vijaya Tirunagaru, Naisargee Shah, Richard Bryce, Robert Doebele. MANTRA: A randomized, multicenter, phase 3 study of the MDM2 inhibitor milademetan (RAIN-32) versus trabectedin in patients with de-differentiated liposarcoma [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P031.

Lessons learnt from MDM2 fluorescence in-situ hybridisation analysis of 439 mature lipomatous lesions with an emphasis on atypical lipomatous tumour/well-differentiated liposarcoma lacking cytological atypia.

Amplification of the murine double minute-2 (MDM2) gene, which is usually detected with fluorescence in-situ hybridisation (FISH), is the key driving event for atypical lipomatous tumours (ALTs)/well-differentiated liposarcomas (WDLs). We sought to determine the concordance between the histopathological findings and MDM2 FISH in the diagnosis of ALT/WDL, and to identify the histological features of MDM2-amplified tumours lacking classic atypia. We performed a retrospective analysis of all mature lipomatous lesions subjected to MDM2 FISH analysis at our institution. MDM2 FISH analysis was performed on 439 mature lipomatous lesions: 364 (82.9%) were negative and 75 (17%) were positive. In 17 of 75 (22.6%) ALTs/WDLs, cytological atypia was not identified on initial histological assessment, thus favouring lipoma. On review, these cases shared common histological features, consisting of a very low number of relatively small stromal cells within the tumour lobules, with mildly coarse chromatin and oval nuclei, admixed with unremarkable adipocytes in a tumour background devoid of fibroconnective septa, areas of fibrosis, or blood vessels. These cells matched the cells in which FISH showed MDM2 amplification. In contrast, 13 cases (3.5%) regarded as suspicious for ALT/WDL on the basis of histology lacked MDM2 amplification and were reclassified following the FISH findings. We conclude that a subset of lipoma-like ALTs/WDLs are not associated with any of the features typically described in ALT/WDL. Our study also showed that tumours >100 mm are more likely to be ALT/WDL; however, a history of recurrence or concerning clinical/radiological features was not significantly associated with classification as ALT/WDL.

Biology and Management of Dedifferentiated Liposarcoma: State of the Art and Perspectives.

Dedifferentiated liposarcoma (DDL) is defined as the transition from well-differentiated liposarcoma (WDL)/atypical lipomatous tumor (ALT) to non-lipogenic sarcoma, which arises mostly in the retroperitoneum and deep soft tissue of proximal extremities. It is characterized by a supernumerary ring and giant marker chromosomes, both of which contain amplified sequences of 12q13-15 including murine double minute 2 (MDM2) and cyclin-dependent kinase 4 (CDK4) cell cycle oncogenes. Detection of MDM2 (and/or CDK4) amplification serves to distinguish DDL from other undifferentiated sarcomas. Recently, CTDSP1/2-DNM3OS fusion genes have been identified in a subset of DDL. However, the genetic events associated with dedifferentiation of WDL/ALT remain to be clarified. The standard treatment for localized DDL is surgery, with or without radiotherapy. In advanced disease, the standard first-line therapy is an anthracycline-based regimen, with either single-agent anthracycline or anthracycline in combination with the alkylating agent ifosfamide. Unfortunately, this regimen has not necessarily led to a satisfactory clinical outcome. Recent advances in the understanding of the pathogenesis of DDL may allow for the development of more-effective innovative therapeutic strategies. This review provides an overview of the current knowledge on the clinical presentation, pathogenesis, histopathology and treatment of DDL.

Development and structural characterisation of human scFv targeting MDM2 spliced variant MDM215kDa

The murine double minute 2 (MDM2) protein is a major negative regulator of the tumour suppressor protein p53. Under normal conditions, MDM2 constantly binds to p53 transactivation domain and/or ubiquinates p53 via its role as E3 ubiquitin ligase to promote p53 degradation as well as nuclear export to maintain p53 levels in cells. Meanwhile, amplification of MDM2 and appearance of MDM2 spliced variants occur in many tumours and normal tissues making it a prognostic indicator for human cancers. The mutation or deletion of p53 protein in half of human cancers inactivates its tumour suppressor activity. However, cancers with wild type p53 have its function effectively inhibited through direct interaction with MDM2 oncoprotein. Here, we described the construction of a MDM2 spliced variant (rMDM215kDa) consisting of SWIB/MDM2 domain and its central region for antibody generation. Biopanning with a human naïve scFv library generated four scFv clones specific to rMDM215kDa. Additionally, the selected scFv clones were able to bind to the recombinant full length MDM2 (rMDM2-FL). Computational prediction showed that the selected scFv clones potentially bind to exon 7–8 of MDM2 while leaving the MDM2/SWIB domain free for p53 interaction. The developed antibodies exhibit good specificity can be further investigated for downstream biomedical and research applications.

A single institutional experience treating adipocytic tumors: incidence, disease-related outcomes, and the clinical significance of MDM2 analysis.

Adipocytic tumors exist either as a benign or malignant form. The benign variant, lipoma, is composed of normal fat tissue. Lipomas typically develop from superficial fat cells beneath the skin or mucous membranes. Liposarcoma, the malignant counterpart, often develops in deeper tissues and is the most commonly diagnosed Soft Tissue Sarcoma (STS), comprising at least 20% of adult STS. However, malignant tumors of fatty origin exist as a spectrum of diagnoses, each carrying a unique risk of recurrence, metastasis, and longterm survival. The World Health Organization classifies liposarcomas into five categories: i) Atypical Lipomatous Tumors/Well Differentiated (ALT/WD); Ii) Dedifferentiated (ALT/DD); Iii) Myxoid; Iv) Round cell; and v) Pleomorphic. Lipomatous tumors often exhibit different immunohistochemical patterns. Benign lipomas are distinguished by the absence of Murine Double-Minute 2 (MDM2) amplification. Similarly, ALT/WD, classically defined as a low-grade and locally aggressive tumor, demonstrates consistent patterns of MDM2 amplification. Some studies suggest 10% of ALT/WD progress to the highgrade DD form, with others report a dedifferentiation rate of as high as 20% for primary ALT/WD based on location. The ALT/DD subtype is aggressive and has a high capacity to metastasize. While the mechanism of pathogenesis of ALT/DD metastasis is unknown, previous studies suggest that increased MDM2 amplification may play a role. This study sought to evaluate a single institutional experience treating the entire spectrum of lipomatous tumors and describe utilization patterns of MDM2 testing. The group hypothesized: i) Atypical Lipomatous Tumors (ALT), which include ALT/DD and ALT/WD, would exhibit a higher rate of local recurrence than lipomas with no significantly increased incidence of metastases; and ii) at least 50% of our MDM2 testing of ALT would prove positive for the MDM2 overamplification. This study retrospectively reviewed 105 cases (66 lipomas, 27 ALTs, 12 liposarcomas) of patients who underwent lipomatous tumor excision at our institution from 2013 to 2017. Twenty-five tumors (6 lipomas, 18 ALT, 1 liposarcoma) were tested for MDM2 amplification. Three of the tested tumors recurred (2 ALT, 1 liposarcoma), and each exhibited MDM2 overamplification. Five tumors (5 liposarcoma) developed late metastases. These data suggest that although ALT is associated with a higher rate of local recurrence, metastases are quite rare. Additionally, the data demonstrate a high rate of positive MDM2 testing (76%) based on clinical and imaging characteristics of the tumors.

MDM2 gene amplification as selection tool for innovative targeted approaches in PD-L1 positive or negative muscle-invasive urothelial bladder carcinoma

AimsAccording to The Cancer Genome Atlas (TCGA), around 9% of bladder carcinomas usually show abnormalities of the murine double minute 2 (MDM2) gene, but a few studies have been investigated...

Comprehensive profiling of MDM2/TP53 genomic aberration in Chinese patients with diverse malignancies.

e13508 Background: Murine double minute-2 (MDM2) has increasing clinic relevance as preclinical and early clinical evidences have showed that the MDM2 inhibitors are promising alternative treatments for patients with MDM2-amplified (-amp) and TP53-wild-type (-WT) tumors by preventing TP53 protein degradation. However, exploration into genomic landscape of MDM2/TP53 across various solid tumors in Chinese patients is still limited. Methods: Formalin-fixed, paraffin-embedded (FFPE) tumor samples were collected from 10010 Chinese patients with solid tumors and subjected to a clinical-grade next-generation sequencing (NGS)-based 450 gene panel testing carried out by a College of American Pathologists (CAP) accredited and Clinical Laboratory Improvement Amendments (CLIA) certified laboratory. Genomic alterations (GAs) including single base substitutions, short and long insertion/deletions (Indels), copy number variations, gene fusions, and rearrangements were analyzed. Tumor mutational burden (TMB) was measured by a NGS algorithm. Results: Amplification of MDM2 occurred in 3.3% of Chinese patients. MDM2-amp was detected most frequently in soft tissue sarcoma (STS, 11.4 %), melanoma (10.3 %) and osteosarcoma (6.3 %). Notably, MDM2-amp was revealed to be mutually exclusive with TP53-mut in most tumor types other than esophageal carcinoma (93.9 %), head and neck carcinoma (68.4%) and ovarian carcinoma (50 %). Tumors with highest frequencies of MDM2-amp/ TP53-WT were melanoma (100%), osteosarcoma (100%) and urothelial carcinoma (100 %). The most common co-altered genes accompanied with MDM2-amp were FRS2 (84%), CDK4 (38%), EGFR (26%), TP53 (17%) and GLI1 (14%). 82.8% patients who had one or more co-alterations potentially targetable with either FDA-approved or investigational agent. Moreover, TMB of MDM2-amp tumors were significantly lower than that of MDM2-WT and MDM2-mutation (-mut) tumors (median TMB: 3.1 vs. 4.6 vs. 10.8, p < 0.001 respectively). Conclusions: MDM2 amplification was found in 3.3% of 10010 Chinese cancer patients, 83.4% of whom harbored wild-type TP53 that were potentially responsive to MDM2 inhibitors. In addition, 82.8% of the patients with MDM2-amp harbored genomic co-alterations and were potentially therapy targetable. This study provided insights into identifying patients who might potentially benefit from anti-MDM2 therapies.

Cardiac Intimal Sarcoma with Complete Response to Thoracic Radiotherapy- A Case Report

Objectives: Sarcomas are the most common primary, cardiac malignant tumours but are, nevertheless, rare (0.001-0.03% of all tumours [1-4]. Intimal sarcomas characterised by Murine Double Minute 2 (MDM2) gene amplification originate from large vessels, but from the heart only very rarely. The prognosis of primary cardiac sarcomas is very poor; no evidence-based management guidelines are available. Surgery is the first-line treatment but is not possible in over 50% of cases. Radiotherapy ensures efficient local control and is indicated as neoadjuvant, adjuvant, and palliative treatment. Materials and Methods: We report the case of a 59-year-old female with a metastatic, cardiac intimal sarcoma identified after symptomatic metastasis to the lower limbs. Imaging revealed a hypermetabolic cardiac mass emerging from the left atrium. Adductor muscle biopsy identified an intimal sarcoma metastasis exhibiting MDM2 gene amplification; the primary site was cardiac. We first prescribed anthracycline chemotherapy and irradiation of the cardiac mass. She received 50 Gy into the planned target volume including the atrial mass (2 Gy per day 5 days per week) delivered via three-dimensional external-beam radiotherapy. Results: The irradiated cardiac mass did not grow during follow-up, rather, stabilising and then gradually decreasing in size, associated with reduced hypermetabolism. Seven months after radiotherapy ceased, she achieved a complete cardiac response, but the metastatic lesions progressed. Her general condition improved. The heart failure signs disappeared and her symptoms became less serious. Conclusion: Radiotherapy should be favoured for patients with cardiac or intimal sarcomas featuring MDM2 amplification. The tumour seems to be radiosensitive, although anthracycline may also have been helpful. Radiotherapy is a valuable tool and could reduce mortality caused by local heart failure.

1732TiP - A phase II biomarker-driven study evaluating the clinical efficacy of an MDM2 inhibitor, milademetan, in patients with intimal sarcoma, a disease with a high unmet need

BackgroundIntimal sarcoma is an extremely rare, high-grade malignant neoplasm arising in the tunica intima of large blood vessels, most frequently the pulmonary arteries and aorta. In human tumors that retain wild-type p53 protein, p53 activity is often inhibited by interaction with murine double minute 2 (MDM2). As MDM2 amplification is found in over 70% of intimal sarcomas, inhibition of MDM2 could provide clinical benefit in this patient population. Milademetan is a novel specific small-molecule inhibitor of MDM2 that disrupts the MDM2-p53 interaction in tumor cells. A cell-free study using recombinant MDM2 and p53 proteins demonstrated inhibition of MDM2-p53 binding by milademetan (IC50: 5.57nM). Treatment with milademetan resulted in a concentration-dependent increase of p21 and PUMA mRNA levels in an osteosarcoma cell line harboring MDM2 gene-amplification. Milademetan also inhibited cell growth in different cell lines with wild-type p53 (GI50s: 0.043 - 0.276μM), but not p53 mutant or null cell lines (GI50s: >10μM). We focus on targeting MDM2-p53 axis with milademetan in patients with intimal sarcoma. Trial designThis is a phase II, open-label, 2-part study at a single site. Eligible patients will be at least 18 years old with intimal sarcoma who also have MDM2 amplification (≧4-fold). Part 1 (safety lead-in cohort) will enroll 3 subjects to evaluate the safety, tolerability, and pharmacokinetics (PK) of milademetan (260mg qdx3 every 14 days twice in a 28-days cycle). Part 2 of the study will enroll an open-ended number of subjects. Overall, enrollment of≥5 subjects with advanced intimal sarcoma is planned in the next 3 years. The primary endpoint of the study is objective response rate which will be assessed in all subjects enrolled in Parts 1 and 2 who have received milademetan. Due to the absence of any effective treatment for intimal sarcoma, at least 1 patient with objective response will be regarded as clinically meaningful. Secondary endpoints include safety, pharmacokinetics, disease control rate, progression-free survival, and overall survival. Enrollment began in Dec 2018. As of 1 Apr 2019, 3 subjects have been enrolled into Part 1. Clinical trial identificationJMA-IIA00402. Legal entity responsible for the studyNational Cancer Center. FundingJapan Agency for Medical Research and Development. DisclosureK. Yonemori: Honoraria (self): Taiho; Honoraria (self): Novartis; Honoraria (self): Eisai; Honoraria (self): Pfizer; Honoraria (self): ONO. T. Shimizu: Advisory / Consultancy: Takeda Oncology; Honoraria (self): Ono Pharmaceutical; Honoraria (institution): Ono Pharma Taiwan CO., LTD.; Honoraria (self): Boehringer Ingelheim; Honoraria (self): Taiho Pharmaceutical ; Honoraria (self): Chugai Pharmaceutical; Research grant / Funding (self): Takeda Oncology; Research grant / Funding (self): PharmaMar; Research grant / Funding (self): Bristol-Myers Squibb Japan; Research grant / Funding (self): Daiichi Sankyo,; Shareholder / Stockholder / Stock options: SymBio Pharmaceuticals; Research grant / Funding (self): Five Prime Therapeutics; Research grant / Funding (self): 3D Medicine; Research grant / Funding (self): Chordia Therapeutics; Research grant / Funding (self): AbbVie; Research grant / Funding (self): AstraZeneca; Research grant / Funding (institution): Eli Lilly; Research grant / Funding (self): Novartis. A. Hirakawa: Advisory / Consultancy: Ono Pharmaceuticals Co., Ltd.; Advisory / Consultancy: Kissei Co., Ltd.; Advisory / Consultancy: AbbVie GK; Advisory / Consultancy: Nippon Boehringer Ingelheim Co., Ltd.; Advisory / Consultancy: Astellas Pharm Inc.; Advisory / Consultancy: Nippon ShinyakuCo., Ltd.; Advisory / Consultancy: Sumitomo Dainippon Pharma Co., Ltd.; Advisory / Consultancy: Torii Pharmaceutical Co. Ltd. S. Fujitani: Full / Part-time employment: DaiichiSankyo. N. Yamamoto: Research grant / Funding (self): Astellas; Speaker Bureau / Expert testimony, Research grant / Funding (self): Chugai; Advisory / Consultancy, Research grant / Funding (self): Eisai; Research grant / Funding (self): Taiho; Speaker Bureau / Expert testimony, Research grant / Funding (institution): BMS; Speaker Bureau / Expert testimony, Research grant / Funding (self): Pfizer; Research grant / Funding (self): Novartis; Speaker Bureau / Expert testimony, Research grant / Funding (self): Eli Lilly; Research grant / Funding (self): AbbVie; Honoraria (self): Daiichi-Sankyo; Research grant / Funding (self): Bayer; Advisory / Consultancy, Research grant / Funding (self): Boehringer Ingelheim; Research grant / Funding (self): Kyowa-Hakko Kirin; Advisory / Consultancy, Research grant / Funding (self): Takeda; Speaker Bureau / Expert testimony, Research grant / Funding (self): ONO; Research grant / Funding (self): Janssen Pharma; Research grant / Funding (self): MSD; Research grant / Funding (self): Merck; Advisory / Consultancy: Otsuka; Advisory / Consultancy: Cimic. Y. Fujiwara: Honoraria (self): Astellas; Honoraria (self): Daiichi-Sankyo; Honoraria (self): BMS; Honoraria (self): SRL. All other authors have declared no conflicts of interest.

Abstract 2061: A novel small molecule inhibitor of MDM2-p53 (APG-115) has antitumor activity in gastric adenocarcinoma

Abstract Background: The amplification of Murine Double Minute 2 (MDM2) and mutation of P53 are significant processes in the incidence of gastric cancer. APG-115, a small molecular inhibitor of MDM2-P53, is a novel potential anticancer agent. We aim to investigate the anticancer effect of APG-115 in gastric cancer. Methods: We selected 87 pairs of gastric cancer tissues (primary tumors and metastatic tissues). Using Immunohistochemistry (IHC) and Fluorescence in situ hybridization (FISH), we examined the expression and amplification of MDM2 and P53. Using MTS, we examined the anti-proliferation activity of APG-115 in five gastric cancer cell lines (AGS, MKN-45, BGC-823, NCI-N87, NUGC-3) by CCK-8 assay. We used western blot analysis and siRNA interference for mechanism exploration to examine the anti-cancer activity of APG-115 in p53 wild type gastric cancer cell lines. Gastric cancer cell xenograft nude mice models were used for in vivo efficacy evaluation. Results: We examined 87 pairs of gastric cancer tissues in IHC. The results suggested that the primary tumors and metastatic tissues with high expression of MDM2 and P53 have shortened survival. The proliferation inhibition of APG-115 on p53 wild-type gastric cancer cells of AGS and MKN45 was concentration and time dependent. APG-115 induced apoptosis in gastric cancer cells. APG-115 can induced cell-cycle arrest in G1/G0 phase in the p53 wild-type of gastric cancer cells. APG-115 exhibited potent antitumor activity against established human gastric cancer xenografts. Conclusions: APG-115 can inhibitor tumor growth in p53 wild-type gastric cancer cells by inducing apoptosis and cell cycle arrest both in vitro and vivo. APG-115 can serve as an effective and precise therapeutic strategy for gastric cancer. Citation Format: Lin Zhang, Luo Qiuyun, Yan Xianglei, Xueping Wan, Luping Yuan, Yuxing Zhang, Suna Zhou, Wentao Pan, Mengxian Pan, Miaozhen Qiu, Shijuan Mai, Dajun Yang. A novel small molecule inhibitor of MDM2-p53 (APG-115) has antitumor activity in gastric adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2061.

A phase Ia/Ib, open label, multicenter, dose-escalation study of BI 907828 (MDM2-p53 antagonist) in adult patients with advanced or metastatic solid tumors.

TPS3166 Background: Inactivation of tumor protein 53 (TP53) is a central mechanism of tumors to promote survival and proliferation. The murine double minute 2 ( MDM2) oncogene is the primary cellular negative regulator of TP53. Small molecule inhibitors of the MDM2-p53 interaction are currently being evaluated in clinical trials as new anti-cancer drugs, and clinical data published to date support the rationale to target MDM2-amplified tumors. BI 907828 is a potent MDM2-p53 antagonist that has shown efficacy in mouse models of human cancer. Methods: NCT03449381 is a Phase 1a/1b, open-label, multicenter, dose-escalation trial of BI 907828 in patients aged ≥18 years with advanced/metastatic solid tumors. Primary objectives of the Phase 1a (dose-escalation) part are to determine: the maximum tolerated dose (MTD) of BI 907828 based on dose-limiting toxicities (DLTs) during the first treatment cycle; the recommended dose for expansion (RDE); safety and tolerability. Patients in Arm A will receive one dose of BI 907828 every 21 days, and patients in Arm B one dose on Days 1 and 8, every 28 days. Secondary objectives include pharmacokinetics (PK), pharmacodynamics (PD) [GDF-15 induction in plasma], and preliminary anti-tumor activity. Primary endpoints are the number of patients with DLTs during the first treatment cycle, and the MTD. Phase 1a will include ≈50 evaluable patients with locally advanced or metastatic solid tumors with either a known TP53 wild type (wt) status or unknown TP53 status, regardless of MDM2 amplification status at the time of study entry. The main objectives of Phase 1b (expansion cohorts) are to assess efficacy, safety, and PK profiles at the RDE, and to determine the recommended dose for Phase 2. The primary endpoint is objective response, where best response is determined according to RECIST v1.1, or RANO criteria for patients with glioblastoma. Phase 1b will include up to 150 evaluable patients with TP53 wt tumors, assigned to four different cohorts, including non-squamous NSCLC, soft tissue sarcoma, glioblastoma, urothelial carcinoma, and solid tumors with brain metastases. As of 8th February 2019, 11 patients have been enrolled. Clinical trial information: NCT03449381.

Degree of MDM2 Amplification Affects Clinical Outcomes in Dedifferentiated Liposarcoma.

Dedifferentiated liposarcomas (DDLPS) are mesenchymal tumors associated with universally poor response to treatment. Genomic amplification of murine double minute 2 (MDM2) is used as a diagnostic biomarker; however, no established biomarkers exist to guide DDLPS treatment. In the largest study of its kind, we report that the extent of MDM2 amplification, not simply the presence of MDM2 amplification, may be biologically important to the actions of DDLPS. The distribution of MDM2 amplification in DDLPS was assessed using data from a commercial sequencing laboratory (n = 642) and The Cancer Genome Atlas (n = 57). Data from two retrospective clinical trials (n = 15, n = 16) and one prospective clinical trial (n = 25) were used to test MDM2's utility as a clinical biomarker. in vitro and in vivo assessments were conducted in DDLPS cell lines. Genomic MDM2 amplification follows a highly reproducible log-normal distribution. In patients with DDLPS treated with complete tumor resection, elevated MDM2 was associated with shortened time to recurrence as measured by genomic amplification (p = .003) and mRNA expression (p = .04). In patients requiring systemic therapy, higher MDM2 amplification was associated with reduced overall survival (p = .04). Doxorubicin treatment of DDLPS cells in vitro demonstrated variable sensitivity based on baseline MDM2 levels, and doxorubicin treatment elevated MDM2 expression. In vivo, treatment with doxorubicin followed by an MDM2 inhibitor improved doxorubicin sensitivity. MDM2 amplification levels in DDLPS follow a reproducible distribution and are associated with clinical outcomes and drug sensitivity. These results suggest that a prospective study of MDM2 as a predictive biomarker in DDLPS is warranted. No validated biomarkers exist for treatment selection in dedifferentiated liposarcoma (DDLPS). Although murine double minute 2 (MDM2) is currently used for diagnosis, the clinical relevance of MDM2 amplification has yet to be fully assessed. This study found that MDM2 amplification follows a predictable distribution in DDLPS and correlates with clinical and biological outcomes. These data suggests that MDM2 amplification may be a useful biomarker in DDLPS.