Eligibility Details:  
        Inclusion Criteria:
          -  Patients with a diagnosis of a primary abdominal malignancy consented to undergo major
             surgery with a planned length of stay of 3 or more days.
          -  Eligible patients must have signed a consent for surgical resection of the malignancy.
          -  Adequate hematological function defined as: platelet count ≥ 100 x 109/L, absolute
             neutrophil count ≥ 1 x 109/L, white blood count ≥ 2.5 x 109/L, hemoglobin count ≥ 90
             g/L.
          -  Adequate organ functioning, including: total bilirubin ≤ 1.5 x upper limit of normal
             (ULN); AST, ALT < 2.5 x ULN; INR <1.5 ; CrCl>30mL/min.
          -  If sexually active, and of childbearing potential, subjects must agree to use
             acceptable birth control from screening until the final study visit (study day, SD35)
             or early termination. Acceptable methods of birth control include: spermicide with
             condom, diaphragm, or cervical cap, IUD (intrauterine device), hormonal contraception,
             vasectomy, and abstinence. (Plan B or the rhythm method are not considered reliable
             methods.
          -  Male subjects should agree to avoid having sex for 5 days before surgery and 10 days
             post surgery taking tadalafil due to the risk of sustained erection
          -  Ability to understand and provide a signed informed consent form (ICF) approved by the
             Institutional Review Board (IRB/IEC/REB).
          -  Ability to comply with protocol requirements.
        Exclusion Criteria:
          -  Prior adjuvant chemotherapy or radiation within 8 weeks of planned surgery.
          -  Pregnant or nursing mothers or women of childbearing potential not using acceptable
             methods of birth control.
          -  Documented significant immunodeficiency due to underlying illness (e.g. HIV/AIDS)
             and/or medication (e.g. systemic corticosteroids, azathioprine, cyclosporin A).
             Subjects may be on physiologic doses of replacement prednisone or equivalent doses of
             corticosteroid (<7.5 mg daily).
          -  History of autoimmune disease (even if controlled with medication) such as but not
             restricted to, inflammatory bowel disease, systemic lupus erythematosus, ankylosing
             spondylitis, scleroderma, or multiple sclerosis.
          -  Allergies or any contraindication to the use of tadalafil or any components of Cialis®
             or the influenza vaccine (including eggs), Agriflu®.
          -  Serious intercurrent chronic or acute illness, or other illness considered by the
             investigator as an unwarranted high risk for an investigational product.
          -  Patients who have suffered a myocardial infarction, stroke, or life-threatening
             arrhythmia within the last 6 months.
          -  Patients with resting hypotension (BP <90/50 at rest) or hypertension (BP >170/110 at
             rest).
          -  Patients with cardiac failure or coronary artery disease causing unstable angina.
          -  Use any type of nitrate drug therapy, including short-acting nitrate-containing
             medications, due to the risk of developing potentially life-threatening hypotension.
             The use of organic nitrates, either regularly and/or intermittently, in any form (e.g.
             oral, sublingual, transdermal, by inhalation) is absolutely contraindicated (see list
             Appendix II).
          -  Use of guanylate cyclase stimulators (cinaciguat or riociguat).
          -  Use of alpha-blocker therapy (see list in Appendix I).
          -  Previous episode of non-arteritic anterior ischaemic optic neuropathy (NAION) or
             history of retinitis pigmentosa.
          -  Use of anti-platelet (excluding ASA) or anti-coagulation medication (Patients who
             discontinue such medications at least 7 days prior to first treatment may be eligible
             for this study).
          -  Use of the following anti-viral agents: ribavirin, adefovir, cidofovir (at least 7
             days prior to the first treatment), and PEG-IFN (at least14 days prior to the first
             treatment).
          -  Active infection of any site requiring ongoing treatment.
          -  Known anatomical deformities of the penis (such as angulation, cavernosal fibrosis or
             Peyronie's disease) or any condition that might predispose the patient to priapism.
          -  History of Guillaine-Barré Syndrome.
          -  Subjects with a medical or psychological impediment to probable compliance with the
             protocol should be excluded.
          -  Active drug or alcohol use or dependence or other conditions that, in the opinion of
             the investigator, would interfere with adherence to study requirements. Social alcohol
             use is acceptable.
          -  Concurrent inhibitors of moderate or strong CYP3A4 inhibitors
          -  Taking any other PDE-5 inhibitor (such as sildenafil) during the active phase of the
             study between enrollment to SD35.
          -  History of lactose or milk sugar intolerance
          -  Liver or Kidney disease
          -  Sickle cell anemia
          -  Peptic ulcer or other bleeding disorders