This is an open label, randomized, two arm, multi-center study to explore the effect of leronlimab on the overall response rate/ overall survival and safety and tolerability when used in combination with trifluridine and tipiracil + bevacizumab in patients with MSS, mCRC who have progressed on prior treatment before participating in the study. The main questions this study aims to answer are:

1. Can leronlimab, in combination with standard of care therapies trifluridine and tipiracil+ bevacizumab, increase the objective response rate in persons with MSS, mCRC who have progressed on prior treatment before participating in the study.
2. Is leronlimab safe and well tolerated in these subjects when used in combination with standard of care therapies trifluridine and tipiracil+ bevacizumab.

This is an open label, randomized, two arm, multi-center study to explore the effect of leronlimab on the overall response rate/ overall survival and the safety and tolerability when used in combination with trifluridine and tipiracil + bevacizumab in patients with MSS, relapsed refractory, mCRC who have received and progressed, or are intolerant, of at least two prior standard of care treatment regimes, which may have included fluoropyrimidine, oxaliplatin, or irinotecan chemotherapy, an anti-VEGF therapy, and, if RAS wild-type and medically appropriate, an anti-EGFR therapy.

This study will enroll approximately 60 participants, 30 participants in each of two arms evaluating either 350 mg or 700 mg of leronlimab, who are 18 years of age or older, with histologically confirmed metastatic colorectal cancer that is microsatellite stable (MSS). Participants will be randomized 1:1 to each arm, where approximately 30 participants will receive 350 mg of leronlimab + trifluridine and tipiracil + bevacizumab and approximately 30 will receive 700 mg of leronlimab + trifluridine and tipiracil + bevacizumab.

Inclusion Criteria:

1. Male or female subjects age ≥ 18 years with a history of treated colorectal cancer with unresectable metastases of the primary colorectal cancer to other organs.

2. If HIV-1 positive, viral load must be < 50 copies/ml and participant must be on stable ART for at least 3 months.

3. Adult patients with metastatic colorectal cancer (mCRC) received and progressed, or are intolerant, of at least two prior standard of care treatment regimes, which may have included fluoropyrimidine-, oxaliplatin-, or irinotecan chemotherapy, an anti-VEGF therapy, and, if RAS wild-type and medically appropriate, an anti-EGFR therapy.

4. Histologically confirmed for microsatellite stable MSS colorectal cancer by PCR, Immunohistochemistry (IHC) or Next-generation sequencing (NGS).

5. Have measurable disease per RECIST 1.1

6. Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

7. Expected survival of at least three months.

8. No anti-cancer treatment within the last two weeks or at least 5 half-lives prior to treatment (whichever is shorter), except for palliative radiation therapy from which the patient has recovered from all adverse events.

9. Patients must have adequate organ and bone marrow function within 28 days prior to the first dosing visit, defined as:

   i. Acceptable liver function:

   1. Total bilirubin ≤ 1.5 × upper limit of normal (ULN) OR direct bilirubin ≤ ULN for participants with total bilirubin levels > 1.5 × ULN (participants with known Gilbert's disease may enroll with Total bilirubin ≤ 2.5 × ULN AND direct bilirubin is ≤1.5 × ULN) (if liver metastases are present, Total bilirubin ≤2.0 × ULN).
   2. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN (≤ 5 × ULN for participants with liver metastases).

   ii. Acceptable renal function:

   a) GFR ≥ 30 mL/min iii. Acceptable hematologic status:

   1. Hemoglobin ≥ 9 g/dL Note: Criteria must be met without packed red blood cell (pRBC) transfusion within the prior 2 weeks. Participants can be on stable dose of erythropoietin (≥ approximately 3 months).
   2. White blood cells > 2500/µL
   3. Absolute neutrophil count > 1500/µL
   4. Platelet count > 100 000/µL.

10. Clinically normal resting 12-lead ECG at Screening Visit or, if abnormal, considered not clinically significant by the Principal Investigator.

    a) No QTC interval exceeding 460 milliseconds (ms) for females, no QTC interval exceeding 450 ms for males.

11. Both male and female patients and their partners of childbearing potential must agree to use two medically accepted methods of contraception (e.g., barrier contraceptives [male condom, female condom, or diaphragm with a spermicidal gel], hormonal contraceptives [implants, injectables, combination oral contraceptives, transdermal patches, or contraceptive rings], or one of the following methods of birth control (intrauterine devices, tubal sterilization or vasectomy) or must practice complete abstinence from intercourse of reproductive potential from study entry to 6 months after the last day of treatment (excluding women who are not of childbearing potential and men who have been sterilized).

12. Females of childbearing potential (FOCBP) must have a negative serum pregnancy test at Screening Visit and negative urine pregnancy test prior to receiving the first dose of study.

13. Male participants must agree to use contraception and refrain from donating sperm for at least 6 months after the last dose of study intervention.

14. Patients must have the ability to understand and the willingness to sign a written informed consent prior to registration on study.

Exclusion Criteria:

1. Known severe hypersensitivity towards monoclonal antibodies.

2. Clinically significant active coronary heart disease and cardiovascular insufficiency with compromised hemodynamics per PI discretion.

3. Had a known additional malignancy that was progressing or had required active treatment within the past [2] years.

   Note: Participants with basal cell carcinoma of the skin, squamous cell carcinoma of the skin, incidentally diagnosed prostate cancer (i.e., during a TURP), carcinoma in situ (breast or cervical), excluding carcinoma in situ of bladder, that had undergone potentially curative therapy are not excluded.

4. Active hepatitis B (defined as having a positive hepatitis B surface antigen [HBsAg] test) or active hepatitis C infection (defined as detectable hepatitis C virus [HCV] RNA), or other known viral infections.

5. Are pregnant or breastfeeding or expecting to conceive or father children within the projected duration of the study, starting with the Screening Visit through 120 days after the last dose of study intervention.

6. Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial.

7. Stroke and/or transient ischemic attack within 6 months prior to screening.

8. Placement of a cardiac stent or bypass surgery within 6 months of screening.

9. Tumor invasion of a large vascular structure (e.g., pulmonary artery, superior or inferior vena cava).

10. Is currently participating in or has participated in a study of an investigational agent or has used an investigational device within 4 weeks prior to the first dose of study treatment.

    Note: Participants who have entered the follow-up phase of an investigational study may participate as long as it has been 4 weeks after the last dose of the previous investigational agent.

11. Active, uncontrolled bacterial, viral, or fungal infections, requiring systemic therapy.

12. Inability to follow protocol.

13. Patients who received Trifluridine + Tipiracil (TAS-102) prior to receiving first study drug dose.

14. Serious non-malignant or malignant disease (e.g. hepatic compromise, obstructive hydronephrosis, or other conditions which may worsen) that could compromise study objectives in the opinion of the investigator, including recurrent ascites or pleural effusion requiring more than one paracentesis or thoracentesis or a single paracentesis or thoracentesis removing more than 3.0 liters of ascites within 30 days prior to screening.