We are doing this study to find out if an experimental drug called ADI-PEG 20 (the study drug) combined with two types of FDA-approved chemotherapies (gemcitabine and docetaxel) is a safe and effective option for people who have leiomyosarcoma.

Leiomyosarcoma

Adults ages 18+ who are diagnosed with leiomyosarcoma.

For more information about who can participate in this study, please contact the study team at alicia.wilkerson@duke.edu.

If you choose to join this study, during the screening period you will:

• Have a physical exam
• Have blood draws
• Have imaging scans (CT or MRI)
• Have an electrocardiogram (ECG) to check your heart function
• Visit the clinic for various tests to see if you are eligible to proceed to the study drug period

If you are eligible for the study drug period, you will get a random assignment (like a coin flip) to 1 of 2 groups:

• Group 1 will receive the study drug in combination with gemcitabine and docetaxel
• Group 2 will receive a placebo (inactive substance with no drug in it) in combination with gemcitabine and docetaxel

The study drug and placebo are given as injections (shots) into a muscle. Gemcitabine and docetaxel are both given as intravenous (IV) infusions into a vein in your arm.

The drug regimen for this study is given in "cycles," which are periods that each last for 21 days (3 weeks). The regimen for the study will work as follows:

• You will get your first dose of the study drug or placebo a week before your first cycle begins
• You will get a shot of the study drug/placebo on the 1st, 8th, and 15th day of each cycle
• You will get gemcitabine on the 1st and 8th days of each cycle
• You will get docetaxel on the 8th day of each cycle

The number of cycles you do during this study will depend on how you respond to your assigned study regimen.