Trial of Perioperative Tadalafil and Influenza Vaccination in Cancer Patients Undergoing Major Surgical Resection of a Primary Abdominal Malignancy

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