Treatment of Milademetan Versus Trabectedin in Patient With Dedifferentiated Liposarcoma

Inclusion Criteria:

* Histologically confirmed DD liposarcoma, with or without a WD component (WD/DD liposarcoma). Note: Patient must be willing to provide an archival tumor tissue sample that is ≤ 3 years old and of adequate quality or willing to provide a fresh pretreatment biopsy sample
* Advanced unresectable (i.e., where resection is deemed to cause unacceptable morbidity or mortality) and/or metastatic WD/DD liposarcoma
* Measurable tumor lesion(s) in accordance with RECIST version 1.1
* Received 1 or more systemic cancer therapy regimens, including at least 1 anthracycline-based regimen, and had radiographic progressive disease (per RECIST version 1.1) within 6 months before the Screening Visit
* Resolution of any clinically relevant toxic effects of prior chemotherapy, surgery, radiotherapy, or hormonal therapy
* ECOG performance status of 0 or 1
* Adequate bone marrow function:

  * Platelet count ≥ 100 × 10\^9/L
  * Hemoglobin ≥ 9.0 g/dL
  * Absolute neutrophil count ≥ 1.5 × 10\^9/L
* Adequate hepatic function:

  * Alanine aminotransferase and aspartate aminotransferase ≤ 3 × upper limit of normal (ULN) if no liver metastases are present; ≤ 5 × ULN if liver metastases are present
  * Total bilirubin ≤ 1.5 × ULN, or ≤ 3 x ULN in the setting of Gilbert's disease

Exclusion Criteria:

* Prior treatment with any mouse double minute 2 (MDM2) inhibitor or trabectedin
* Other primary malignancies that have required systemic antineoplastic treatment within the previous 2 years, except for localized cancers that have apparently been cured
* Gastrointestinal conditions that could affect the absorption of milademetan, in the opinion of the Investigator
* Uncontrolled infection within the last 7 days requiring IV antibiotics, antivirals, or antifungals
* Known HIV infection or active Hepatitis B or C
* Untreated brain metastases. Note: Patients who require steroids for brain metastases must be on a stable or tapering dose of corticosteroids for at least 2 weeks before randomization. If applicable, patients must complete stereotactic radiosurgery 7 days before and whole brain radiotherapy 21 days before their first dose of study drug.
* Investigational therapy administered within the 28 days or 5 half lives:

  1. Cytochrome P450 3A4 isozyme strong inhibitor: 5 elimination half-lives
  2. CYP3A strong or moderate inducers: 4 weeks
  3. Systemic anticancer therapy or investigational therapy 3 weeks or 5 half-lives,
  4. Immunotherapy with checkpoint inhibitor: 4 weeks
* Curative-intent radiation therapy ≤ 4 weeks or palliative radiation therapy,
* Uncontrolled or significant cardiovascular disease:

  1. QTcF at rest, where the mean QTcF interval is \> 480 milliseconds
  2. Myocardial infarction within 6 months
  3. Uncontrolled angina pectoris within 6 months
  4. New York Heart Association Class 3 or 4 congestive heart failure
  5. Uncontrolled hypertension