Abbreviated Inclusion Criteria:

          1. Be ≥ 18 years of age on day of signing the informed consent

          2. Experienced disease progression during or after standard therapy or were intolerant of
             standard therapy, and for whom no appropriate therapies are available (based on the
             judgment of the Investigator). (Exception: patients in combination expansion cohorts
             please refer to inclusion criteria 12 and 13)

          3. Histological or cytological evidence of advanced, relapsed, or refractory solid tumor
             cancer that is not a candidate for curative therapy

          4. For all patients in the combination expansion cohorts, have at least one lesion that
             is measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 as
             assessed by local site Investigator/radiology. The measurable lesion must be outside
             of a radiation field if the participant received prior radiation. Lesions situated in
             a previously irradiated area are considered measurable if progression has been
             demonstrated in such lesions.

          5. Have tumor tissue that is accessible for pretreatment and on treatment biopsy in the
             opinion of the Investigator and be willing to undergo pretreatment and on-treatment
             biopsies per protocol (for patients in the monotherapy tumor biopsy expansion cohort
             only)

          6. Adequate renal function, defined as serum creatinine clearance ≥ 30 mL/min per
             Cockcroft-Gault formula

          7. Total bilirubin ≤ 1.5 x upper limit of normal (ULN) (≤ 3 x ULN if elevated because of
             Gilbert's syndrome); patients to be treated with SRF617 in combination with
             albumin-bound paclitaxel must have total bilirubin ≤ 1.5 × ULN)

          8. Aspartate aminotransferase and alanine aminotransferase < 2.5 x ULN (< 5 x ULN if
             liver metastasis is present)

          9. Adequate hematologic function, defined as absolute neutrophil count (ANC) ≥ 1.0 x
             109/L, hemoglobin ≥ 8.0 g/dL, and platelet count ≥ 75 x 109/L. Blood cell transfusion
             to meet enrollment criteria is not allowed

         10. Prothrombin time (PT) or international normalized ratio (INR) and activated partial
             thromboplastin time (aPTT) ≤1.5 × ULN unless the patient is receiving anticoagulant
             therapy as long as PT or aPTT is within therapeutic range of intended use of
             anticoagulants

         11. Eastern Cooperative Oncology Group performance status of 0 to 1

         12. For the SRF617 + gemcitabine + albumin-bound paclitaxel safety expansion cohort only:

               1. Patients with confirmed advanced PDAC naive to any prior treatment

               2. Prior neoadjuvant therapy for PDAC is permitted if neoadjuvant therapy was
                  completed at least 6 months prior to study enrollment

               3. Patients initially diagnosed with locally advanced PDAC who have undergone
                  chemotherapy then resection and had no evidence of disease are eligible if
                  relapse or metastatic disease has occurred and if the last dose of chemotherapy
                  was received more than 6 months before study entry

         13. For the SRF617+ pembrolizumab safety expansion cohort only:

               1. Patients with Stage IV unresectable locally advanced or metastatic HER2 GEJ who
                  have received a maximum of one prior line of anticancer therapy

               2. Patients must be anti PD(L)-1 treatment naïve

         14. Willingness of male and female patients who are not surgically sterile or
             postmenopausal to use medically acceptable methods of birth control for the duration
             of the study treatment period (or beginning 14 days before the initiation of
             pembrolizumab for oral contraception), including 30 days after the last dose of
             SRF617, or 120 days after the last dose of pembrolizumab for patients in the SRF617 +
             pembrolizumab cohort; male patients must refrain from donating sperm during this
             period. Sexually active men, and women using oral contraceptive pills, should also use
             barrier contraception with spermicide. Azoospermic male patients and WCBP who are
             continuously not heterosexually active are exempt from contraceptive requirements;
             however, female patients must still undergo pregnancy testing as described in this
             section.

        Abbreviated Exclusion Criteria:

          1. Previously received an anti-CD39 antibody or anti-CD39 targeted therapy

          2. History of Grade 3 allergic or anaphylactic reaction to any monoclonal antibody
             therapy (mAb), or any excipient in the study drugs

          3. Major surgery within 4 weeks before Screening

          4. Unstable or severe uncontrolled medical condition (eg, unstable cardiac function,
             unstable pulmonary condition including pneumonitis and/or interstitial lung disease,
             uncontrolled diabetes) or any important medical illness or abnormal laboratory finding
             that would, in the Investigator's judgment, increase the risk to the patient
             associated with his or her participation in the study

          5. Discontinuation from previous therapy with an anti PD-1, anti-PD-L1, or anti-
             programmed cell death ligand 2 (PD-L2) agent or with an agent directed to another
             stimulatory or co inhibitory T-cell receptor (eg, cytotoxic T-lymphocyte-associated
             protein 4 [CTLA-4], OX 40, CD137) due to a Grade 3 or higher immune-related AE

          6. For patients in the SRF617 + pembrolizumab combination cohort only, prior therapy with
             anti-PD-1 or anti-PD-L1 agents is not permitted

          7. Received prior systemic anti-cancer therapy including investigational agents within 4
             weeks before the first dose of study drug Note: For the SRF617+ gemcitabine+
             albumin-bound paclitaxel safety expansion cohort only, prior systemic anticancer
             therapy (except for neoadjuvant therapy) is not permitted

          8. Currently participating in or has participated in a study of an investigational agent
             or has used an investigational device within 4 weeks before the first dose of study
             drug Note: Patients who have entered the follow-up phase of an investigational study
             may participate if it has been at least 4 weeks after the last dose of the previous
             investigational agent

          9. Received prior radiotherapy within 2 weeks of start of study treatment. Patients must
             have recovered from all radiation-related toxicities, not require corticosteroids, and
             not have had radiation pneumonitis. A 1-week washout is permitted for palliative
             radiation (≤ 2 weeks of radiotherapy) to non-central nervous system disease.

         10. Has received radiation therapy to the lung that is >30Gy within 6 months of the first
             dose of study treatment

         11. Current pneumonitis or history of (non-infectious) pneumonitis requiring steroids