Inclusion Criteria:
1. Patients aged 20 - 80 years old at the time of signing the ICF.
2. Patients with pathologically proved adenocarcinoma of pancreatic cancer and diagnosed with inoperable/metastatic disease (previous systemic chemotherapy, neoadjuvant or adjuvant gemcitabine are acceptable, unless exclusion criteria met).
3. Eastern Cooperative Oncology Group (ECOG) performance status of 1 to 2.
4. Adequate hematologic function defined as: absolute neutrophil count (ANC) \>= 2,000/μL; platelets count \>= 100,000/μL; hemoglobin must be \>= 10 g/dL (can be corrected by growth factor or transfusion).
5. Adequate hepatic function defined as: serum bilirubin =\< 1.5-fold upper limit of normal (ULN); aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) =\< 3-fold ULN (5-fold ULN if liver metastasis is observed).
6. Adequate renal function with: serum creatinine =\< 1.3 mg/dL or calculated creatinine clearance \>= 60 mL/minute according to the Cockcroft and Gault formula.
7. At least one measurable disease according to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.
8. Women must be either of non-child bearing potential, or women with child-bearing potential agree to use effective a highly contraceptive method or a contraceptive implant, exception of hormonal contraception (estrogen/progesterone), during treatment from time of Screening Visit and after cessation of therapy at least 3 months.
9. Planning to receive Gemcitabine monotherapy.
10. Willing and able to comply with all aspects of the treatment protocol.
11. Provide written informed consent.
Exclusion Criteria:
1. Patients with following treatment prior to Gemcitabine monotherapy: chemotherapy, immunotherapy, or biologic systemic anticancer therapy within 28 days of study entry.
2. Pancreatic patients with prior history of Gemcitabine chemotherapy.
3. Women who are pregnant or breastfeeding.
4. Patients with brain metastasis.
5. Patients with bone metastasis alone.
6. Patients with autoimmune disease that requires systemic steroids or immunosuppression agents.
7. Current enrollment in another clinical study or used any investigational drug or device within the past 28 days preceding informed consent.
8. Known history of human immunodeficiency virus (HIV) infection.
9. Existing anticancer treatment-related toxicities of Grades \>= 2 (except for alopecia and neuropathy) according to Common Terminology Criteria for Adverse Events (CTCAE v4.03).
10. Patients with an active infection requiring systemic therapy.
11. Patients are hepatitis C virus (HCV) carrier, and/or with active viral disease which is defined as hepatitis B virus (HBV) carrier with HBV DNA \> 2,000 IU/ml plus AST and ALT \> 3-fold ULN.
12. History of concomitant medical conditions or infectious diseases that, in the opinion of the investigator, would compromise the patient's ability to safely complete the study.
13. Ascertained hypersensitivity to investigational product, Gemcitabine or any of the excipients used in the study.
14. Uncontrolled nausea or vomiting or any symptom that would prevent the ability to comply with daily BLEX 404 Oral Liquid treatment.
15. Judged to be not applicable to this study by investigator such as difficulty of follow-up observation, psychiatric disorder, with any other serious diseases/medical history.
