A Study of STI-3031 (an Anti-PD-L1 Antibody) in Patients With Selected Relapsed/Refractory Malignancies

Inclusion Criteria: * Documented histologically confirmed diagnoses of Extranodal NK/T-cell lymphoma, Peripheral T-cell lymphoma, Diffuse Large B-cell lymphoma (with a PD-L1 gene abnormality or Epstein-Barr virus positivity, or biliary tract cancer. * Prior treatment: * Extranodal NK/T-cell lymphoma: Must have received at least 1 previous line of systemic therapy including an asparaginase-based regimen. * Peripheral T-cell lymphoma: must have received at least 1 previous line of systemic multi-agent chemotherapy. Participants with anaplastic large cell lymphoma (ALCL) must have received brentuximab vedotin * Diffuse Large B-cell lymphoma: Must have received at least 2 previous lines of systemic therapy including an anti-CD20 antibody * Biliary Tract Cancer: Must have received at least 1 previous line of systemic therapy including gemcitabine with or without platinum * Documented disease progression during or after the last therapy * If not previously treated with transplant, Investigator considers the participant ineligible for transplant * Measurable disease * Adult age (as defined by respective country) at time of signing informed consent form (ICF) * Must be able to understand the nature of the study and provide a signed and dated, written ICF prior to any study-specific procedures, sample collections and analyses * Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) score of 0 or 1 * Prior radiotherapy is allowed if more than 14 days have elapsed since the end of treatment and radiopharmaceuticals are permitted if more than 8 weeks have elapsed since the end of treatment * At least 14 days or 5 half-lives must have elapsed since the last chemotherapy, immunotherapy, biological or investigational therapy, and have recovered from toxicities associated with such treatment to \< Grade 2 * Adequate hematologic, renal and hepatic function * Females of childbearing potential (FCBP) must agree to use a reliable form of contraceptive during the study treatment period and for at least 90 days following the last dose of study intervention * Male participants must agree to use barrier contraception (i.e., condoms) for the duration of the study and for at least 90 days after the last dose of study intervention * Predicted life expectancy of at least 16 weeks Exclusion Criteria: * Current participation in another therapeutic clinical trial * Prior treatment with an anti-PD-L1 or anti-PD-1 antibody * Patients with symptomatic central nervous system (CNS) metastases unless considered adequately treated and controlled for at least 2 weeks * Prior hematopoietic stem cell transplantation * History of other previous cancer that would interfere with the determination of safety or efficacy * Any active autoimmune disease or a documented history of autoimmune disease, or history of syndrome that required systemic steroids or immunosuppressive medications, except for participants with vitiligo, hormone replacement therapy for stable thyroid diseases and Type 1 diabetes mellitus * Apparent active or latent tuberculosis (TB) infection * Seropositive for or have active infection with hepatitis C virus (HCV), unless HCV viral load is below the limit of quantification and participant is on concurrent viral suppressive therapy * Seropositive for or have active viral infection with hepatitis B virus (HBV), unless HBV viral load is below the limit of quantification and participant is on concurrent viral suppressive therapy * Seropositive for or active viral infection with HIV, unless the following are met: * CD4+ T-cell (CD4+) counts ≥ 350 cells/uL; and * Participant has been on established antiretroviral therapy (ART) for at least 4 weeks prior to screening and have HIV viral load \< 400 copies/mL; and * Participant has not had acquired immunodeficiency syndrome (AIDS)-defining opportunistic infections within the past 12 months prior to screening * Active infection (viral, bacterial, or fungal) requiring intravenous (IV) systemic therapy within 14 days * Evidence of bleeding diathesis or coagulopathy. * Significant proteinuria * Conditions requiring chronic steroid use (\> 10 mg/day of prednisone or equivalent). * Recent history of attenuated viral vaccination within 30 days prior to the first dose of study intervention * Herbal preparations/medications are not allowed throughout the treatment period unless first discussed with and approved by the Medical Monitor * History of severe hypersensitivity reactions to other monoclonal antibodies or known hypersensitivity to the study intervention or its excipients. * Known current drug or alcohol abuse * Major surgical procedures ≤ 28 days prior to the first dose of study intervention, or minor surgical procedures ≤7 days prior to the first dose of study intervention * Pregnant or lactating * Any of the following cardiac diseases currently or within the last 6 months: * QT interval corrected using Fridericia's formula \>450 milliseconds in men and \> 470 milliseconds in women (up to 480 milliseconds may be allowed after discussion between the Investigator and the Medical Monitor). * Left Ventricular Ejection Fraction (LVEF) \<45% as determined by Multiple Gated acquisition (MUGA) scan or echocardiogram (ECHO) * Unstable angina pectoris * Congestive heart failure (New York Heart Association ≥ Grade 2) * Acute myocardial infarction * Clinically significant conduction abnormality not controlled with pacemaker or medication * Significant ventricular or supraventricular arrhythmias (Participants with chronic rate-controlled atrial fibrillation in the absence of other cardiac abnormalities are eligible.) * Underlying medical conditions that, in the opinion of the investigator and/or medical monitor, will render the administration of study drug hazardous or obscure the interpretation of safety or efficacy results