Key Inclusion Criteria for all Individuals:
* Histologically confirmed advanced or metastatic solid tumor that is measurable or nonmeasurable.
* Eastern Cooperative Oncology Group (ECOG) performance status score of 0, 1, or 2.
* Adequate hematologic counts without transfusional or growth factor support within 2 weeks of study drug initiation (hemoglobin ≥ 9 g/dL, absolute neutrophil count (ANC) ≥1,500/mm\^3, and platelets ≥ 100,000/ μL).
* Creatinine clearance ≥ 30 mL/min as assessed by the Cockcroft-Gault equation.
Key Inclusion Criteria for Individuals with Normal Hepatic Function:
* Normal hepatic function (total bilirubin ≤ ULN and aspartate aminotransferase (AST) ≤ 3.0× ULN).
Key Inclusion Criteria for Individuals with Moderate Hepatic Function:
* Moderate hepatic impairment (1.5 × ULN \< total bilirubin ≤ 3.0 × ULN and any level of AST).
* For individuals with hepatic encephalopathy, the condition does not, in the Investigator's opinion, interfere with the individual's ability to provide an appropriate informed consent.
Key Exclusion Criteria for all Individuals:
* Have poor venous access.
* Donated or lost 500mL or more of blood volume (including plasmapheresis) to plans to donate during the study.
* Have had a prior anticancer biologic agent within 4 weeks prior to Day 1 or have had prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to Day 1 and who have not recovered (i.e., ≤ Grade 1) from adverse events (AEs) at the time of study entry. Individuals participating in observational studies are eligible.
* Had prior treatment with irinotecan within 4 weeks prior to Day 1.
* Have not recovered (i.e., ≤ Grade 1) from AEs due to a previously administered agent.
* Have an active second malignancy.
* Have known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Individuals with previously treated brain metastases may participate provided they have stable CNS disease for at least 4 weeks prior to the first dose of study drug and all neurologic symptoms have returned to baseline, have no evidence of new or enlarging brain metastases, and are taking \< 20 mg/day of prednisone or its equivalent. All individuals with carcinomatous meningitis are excluded regardless of clinical stability.
* Have history of cardiac disease.
* Have active chronic inflammatory bowel disease (ulcerative colitis or Crohn's disease) or gastrointestinal (GI) perforation within 6 months of enrollment.
* Have active serious infection (Contact medical monitor for clarification).
* High-dose systemic corticosteroids (≥20 mg of prednisone or its equivalent) are not allowed within 2 weeks of Check-In. However, inhaled, intranasal, intra-articular, and topical steroids are allowed.
* Use of strong inhibitor or inducer of UGT1A1.
* Have a known history of Gilbert's disease.
Key Exclusion Criteria for Individuals with Normal Hepatic Impairment:
* Must have pre-existing condition interfering with hepatic and/or renal function that could interfere with the metabolism and/or excretion of the study drug.
Key Exclusion Criteria for Individuals with Moderate Hepatic Impairment:
* Had a significant clinical exacerbation of liver disease symptoms within the 2-week period before administration of study drug (i.e., abdominal pain, nausea, vomiting, anorexia, or fever).
* Had clinically demonstrable, tense ascites.
* Had evidence of acute viral hepatitis within 1 month prior to administration of study drug.
* Have evidence of hepatorenal syndrome.
* Individuals with transjugular intrahepatic portosystemic shunt (TIPS) placement.
* Have active Stage 3 or 4 encephalopathy.
