The purpose of this study is to find out if Ivonescimab is an effective and safe treatment that causes few or mild side effects for people with advanced/unresectable leiomyosarcoma.

Inclusion Criteria:

• Male or female age ≥ 18 years at the time of informed consent

• Subjects must have a histologically confirmed unresectable/metastatic LMS

• Be willing and able to provide written informed consent/assent for the trial

• Be willing to comply with treatment protocol

• Adequate performance status: ECOG 0 - 2

• Subjects must have had at least 1 but not more than 3 prior lines of systemic therapy for their LMS. Patients who decline the standard of care first-line systemic therapy will be eligible for this trial. Prior adjuvant therapy will not count provided it was completed more than 6 months previously.

• Patients who were treated with radiotherapy must have completed radiation therapy at least 2 weeks before the study drug administration.

• Patients who were treated with chemotherapy or any investigational therapies or other anti-cancer agent, if eligible, must have been completed at least 3 weeks or at least 5 half-lives (whichever is longer, but no less than 3 weeks) before the study drug administration. All AEs must be ≤ NCI CTCAE v5 Grade 1, except alopecia and stable neuropathy, which must have resolved to Grade ≤ 2 or baseline. Patients who were treated with estrogen modulating therapies (aromatase inhibitors, tamoxifen, GnRH agonists etc.) must have been treated at least 2 weeks prior to study drug administration.

• Participants must have sufficient archival tumor tissue available (most recently procured sample where tissue is available) for research purposes. If archival tumor tissue is insufficient, a pre-treatment research biopsy will be optional but strongly encouraged, if safe and feasible, in the opinion of the Investigator. If biopsy is not feasible and no sufficient archival tissue is available, discussion is required with the Principal Investigator.

• Presence of measurable disease per RECIST v1.1. Target lesions must not be chosen from a previously irradiated field unless there has been radiographically and/or pathologically documented tumor progression in that lesion prior to enrollment.

• Adequate Organ Function:

  a. Hematology (no blood transfusions or growth factor therapy used within 7 days of the screening CBC): i. Absolute neutrophil count (ANC) ≥ 1.5 × 10^9/L

ii. Platelet count ≥ 100 × 10^9/L

iii. Hemoglobin ≥ 9.0 g/dL

b. Kidneys:

i. Creatinine clearance* (CrCL) ≥ 50 mL/min using the Cockcroft-Gault formula or estimated glomerular filtration rate (eGFR) value ≥30 mL/min using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation (adjustment by BSA is not required for eGFR) CrCL or eGFR can be determined using the calculator from the National Kidney Foundation website (www.kidney.org).

ii. Urine protein < 2+ or 24-hour urine protein quantification < 1.0 g

c. Liver:

i. Serum total bilirubin (TBIL) ≤ 1.5 × upper limit of normal (ULN); For patients with liver metastases or confirmed/suspected Gilbert syndrome, TBIL ≤3 × ULN

ii. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN; For patients with liver metastases, AST and ALT ≤ 5 × ULN

• Coagulation: prothrombin time (PT) or international normalized ratio (INR) ≤ 1.5 × ULN, and partial prothrombin time (PTT) or activated partial thromboplastin time (aPTT) ≤ 1.5 × ULN (unless abnormalities are unrelated to coagulopathy). This applies only to patients who are not on therapeutic anti-coagulation. Patients receiving therapeutic anti-coagulation should be on a stable dose.
• Female patients of childbearing age must have negative serum pregnancy test results before randomization or per region-specific guidance documented in the informed consent and a negative urine pregnancy test on the day of first dose prior to dosing.
• Female patient of childbearing potential having sex with an unsterilized male partner must agree to use a highly effective method of contraception from the beginning of screening until 90 days after the last dose of the ivonescimab.
• Unsterilized male patients having sex with a female partner of childbearing potential, or a pregnant or breastfeeding partner must agree to use barrier contraception (male condom) for the duration of the treatment period until 90 days after the last dose of ivonescimab. Male patients with female partners of childbearing potential must have the female partner agree to use at least 1 form of highly effective contraception for the duration of the treatment period until 90 days after the last dose of ivonescimab.

Exclusion Criteria:

• Prior therapy with an anti PD1/PDL1 inhibitor and/or VEGF inhibitor (including multi-tyrosine kinase inhibitors with VEGF inhibition such as pazopanib/cabozantinib/sunitinib).

• History or evidence of symptomatic autoimmune disease (e.g., pneumonitis, glomerulonephritis, vasculitis, or other), or history of active autoimmune disease that has required systemic treatment (i.e., use of corticosteroids, immunosuppressive drugs or biological agents used for treatment of autoimmune diseases) in past 2 years prior to enrollment. Replacement therapy (e.g., thyroxine for hypothyroidism, insulin for diabetes or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency) is not considered a form of systemic treatment for autoimmune disease.

• Evidence of clinically significant immunosuppression such as the following: o Primary immunodeficiency state such as Severe Combined Immunodeficiency Disease o Concurrent opportunistic infection o Receiving systemic immunosuppressive therapy (> 2 weeks) including oral steroid doses > 10 mg/day of prednisone or equivalent within 7 days prior to enrollment. However, in the setting of non-immune mediated indications for steroid use, chronic/active low dose steroid use may be permitted at the discretion of the principal investigator. The dose of steroid allowed in this setting is also at the discretion of the principal investigator. (Use of inhaled or topical steroids is permitted.)

• Major surgical procedures or serious trauma within 4 weeks prior to randomization, or plans for major surgical procedures within 4 weeks after the first dose (as determined by the investigator). Minor local procedures (excluding central venous catheterization and port implantation) within 3 days prior to randomization.

• History of bleeding tendencies or coagulopathy and/or clinically significant bleeding symptoms or risk within 4 weeks prior to randomization, including but not limited to:

  1. Hemoptysis (defined as coughing up ≥ 0.5 teaspoon of fresh blood or small blood clots) Note: transient hemoptysis associated with diagnostic bronchoscopy is allowed.
  2. Nasal bleeding /epistaxis (bloody nasal discharge is allowed)
  3. Current use of prophylactic or full-dose anticoagulants or anti-platelet agents for therapeutic purposes that is not stable prior to randomization is not allowed. The use of full-dose anticoagulants is permitted as long as the international normalized ratio (INR) or activated partial thromboplastin time (aPTT) is within therapeutic limits according to the medical standard of the enrolling institution.

Poorly controlled hypertension with repeated systolic blood pressure ≥ 150 mmHg or diastolic blood pressure ≥ 100 mmHg after oral antihypertensive therapy

• Active autoimmune or lung disease requiring systemic therapy (eg, with disease modifying drugs, prednisone >10 mg daily or equivalent, immunosuppressant therapy) within 2 years prior to randomization, however the following will be allowed:

  1. Replacement therapy (eg, thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency) is permitted.
  2. Intermittent use of bronchodilators, inhaled corticosteroids, or local corticosteroid injections is permitted

• History of major diseases before randomization, specifically:

  1. Unstable angina, myocardial infarction, congestive heart failure (New York Heart Association [NYHA] classification ≥ grade 2) or unstable vascular disease (eg, aortic aneurysm at risk of rupture, Moyamoya disease) that required hospitalization within 12 months prior to randomization, or other cardiac impairment that may affect the safety evaluation of the study drug (eg, poorly controlled arrhythmias, myocardial ischemia)
  2. History of esophageal gastric varices, severe ulcers, wounds that do not heal, abdominal fistula, intra-abdominal abscesses, or acute gastrointestinal bleeding within 6 months before randomization
  3. History of any grade arterial thromboembolic event, Grade 3 and above venous thromboembolic event, as specified in National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) 5.0, transient ischemic attack, cerebrovascular accident, hypertensive crisis, or hypertensive encephalopathy within 12 months prior to randomization
  4. Acute exacerbation of chronic obstructive pulmonary disease within 4 weeks before randomization
  5. History of perforation of the gastrointestinal tract and/or fistula, history of gastrointestinal obstruction (including incomplete intestinal obstruction requiring parenteral nutrition), extensive bowel resection (partial colectomy or extensive small bowel resection) within 6 months prior to randomization

• Imaging during the screening period shows that the patient has:

  1. Radiologically documented evidence of major blood vessel invasion (central pulmonary artery, central pulmonary veins, aorta, brachiocephalic artery, common carotid artery, subclavian artery, superior vena cava) or tumor invading organs (heart, trachea, esophagus, central bronchi [not including segmental bronchi]) or if there is a risk of esophagotracheal or esophagopleural fistula in the opinion of the investigator.
  2. Radiographic evidence of major blood vessel encasement with narrowing of the vessel or intratumor lung cavitation or necrosis that the investigator determines will pose a significantly increased risk of bleeding.

• Symptomatic CNS metastases, CNS metastases with hemorrhagic features, CNS metastasis ≥ 1.5 cm, CNS radiation within 7 days prior to randomization, potential need for CNS radiation within the first cycle, or leptomeningeal disease.

Note: Patients must have stopped corticosteroids or be on physiologic corticosteroid replacement therapy (prednisone ≤ 10 mg daily or equivalent)

• Live vaccine or live attenuated vaccine within 4 weeks prior to planned randomization, or if scheduled to receive a live vaccine or live attenuated vaccine during the study period. Inactivated vaccines are permitted.
• Severe infection within 4 weeks prior to randomization, including but not limited to comorbidities requiring hospitalization, sepsis, or severe pneumonia; active infection (as determined by the investigator) requiring systemic anti-infective therapy within 2 weeks prior to randomization (excluding antiviral therapy for hepatitis B or C)
• Has pre-existing peripheral neuropathy that is ≥ Grade 2 by CTCAE version 5
• Uncontrolled pleural effusions, pericardial effusions, or ascites that is clinically symptomatic Note: Patients managed with indwelling catheters (eg, PleurX) are allowed.
• History of non-infectious pneumonia requiring systemic corticosteroids, or current interstitial lung disease
• Active or prior history of inflammatory bowel disease (eg, Crohn's disease, ulcerative colitis, or chronic diarrhea)
• Known history of human immunodeficiency virus (HIV) whose viral load is not controlled.
• Current use of systemic corticosteroids (>10 mg daily prednisone or equivalent)
• Known history of allogeneic organ transplantation or allogeneic hematopoietic stem cell transplantation
• Patients with active hepatitis B are required to have stable or declining levels of hepatitis B DNA by polymerase chain reaction (PCR) on appropriate anti-viral therapy with acceptable tolerability for one month prior to randomization. All patients with active hepatitis C (hepatitis C virus [HCV] antibody positive with HCV RNA levels above the lower limit of detection) are excluded.
• Known allergy to any component of any study drug; known history of severe hypersensitivity to other monoclonal antibodies
• History or current evidence of any condition (medical [including adverse events from prior anticancer therapy, disorders secondary to tumor], surgical or psychiatric [including substance abuse]), or laboratory abnormality that might confound the results of the study, interfere with the patient's participation for the full duration of the study, might lead to higher medical risk and/or is not in the best interest of the patient to participate, in the opinion of the treating investigator.
• Patient is breastfeeding or plans to breastfeed during the study.

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.