Inclusion Criteria:  Provision of signed and dated, written informed consent prior to any study-specific procedures, sampling, and analyses. Aged at least 18 years as of the date of consent. Histological or cytological confirmation of a solid malignant tumor that has relapsed from or refractory to standard therapies. Estimated life expectancy of a minimum of 12 weeks. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 at ICF signature. Females should be using adequate contraceptive measures until 180 days after the end of treatment, should not be breastfeeding. Male subjects should be willing to use barrier contraception, ie condoms, for the duration of the study and 180 days after the final dose of study treatment.  Exclusion Criteria:  Primary central nervous system disease, central nervous system metastatic disease, leptomeningeal disease, or metastatic cord compression. Prior exposure to a CD73 inhibitor/antibody or adenosine receptor inhibitor. Patients considered to have rapidly progressive disease (from the starting of prior line therapy to disease progression lasting no more than 90 days). Prior therapy with any chemotherapy, immunotherapy, anticancer agents or investigational products from a previous clinical study within 28 days of the first dose of study treatment or within a period during which the investigational product or systemic anticancer treatment has not been cleared from the body. Radiotherapy with a wide field of radiation within 28 days, or radiotherapy with a limited field of radiation for palliation within 14 days of the first dose of study treatment. Subject must have recovered from all radiation related toxicity, not requiring corticosteroids. Prior major surgery (excluding placement of vascular access) within 28 days of the first dose of study treatment or minor surgical procedures ≤7 days. Except for alopecia, any unresolved toxicities from prior therapy greater than Common Terminology Criteria for Adverse Events (CTCAE 5.0) Grade 1 at the time of ICF signature. Subjects receiving unstable or increasing doses of corticosteroids. As judged by the Investigator, any evidence of severe or uncontrolled systemic diseases, including uncontrolled hypertension defined as a blood pressure (BP) ≥160/100 mmHg despite medical therapy, unstable or uncompensated respiratory and renal disease, active bleeding diseases, allogeneic stem cell transplantation, or any solid organ transplant, etc.