Irreversible Electroporation (IRE) Followed by Nivolumab in Patients With Metastatic Pancreatic Cancer.

Inclusion Criteria: * Written informed consent according to Swiss law and ICH GCP E6(R2) regulations before registration and prior to any trial specific procedures. * Pathologically proven PDAC with liver metastases either by histology or cytology. * Liver metastases fulfilling the following criteria: 1. measurable per RECIST v 1.1 (Appendix 1), AND 2. at least two metastases ≥ 1 cm AND 3. percutaneously accessible for repeat biopsy, AND 4. one of the biopsied metastases can be treated with IRE. * At least stable disease after the completion of 10-24 weeks of first line standard chemotherapy (either (m)FOLFIRINOX or Gemcitabine/Abraxane) as confirmed by tumor assessment within 21 days prior to registration OR at least stable disease after the completion of 10-24 weeks of second line standard chemotherapy (either (m)FOLFIRINOX or Gemcitabine/Abraxane) as confirmed by tumor assessment within 21 days prior to registration. The choice of chemotherapy regimen is based on the decision of the treating medical oncologist. * Patients with a prior malignancy and treated with curative intention are eligible if all treatment of that malignancy was completed at least 2 years before registration and the patient has no evidence of that disease at registration. Note: Less than 2 years is acceptable for malignancies with low risk of recurrence and/or no late recurrence. * Patients must be willing to participate in the translational research part of the trial and to undergo a tumor biopsy of the primary tumor and of the two metastatic sites in the liver before trial treatment and after five cycles of nivolumab treatment. * Patients must be willing to travel to the hospital where IRE and biopsy will be performed (Claraspital Basel). * Age ≥ 18 years * WHO performance status 0-1 * Life expectancy ≥4 months * Adequate bone marrow function: neutrophil count ≥ 1.0 x 109/L, platelet count ≥ 100 x 109/L, hemoglobin ≥ 80 g/L * Adequate hepatic function: total bilirubin ≤ 1.5 x ULN (except for patients with Gilbert's disease ≤ 3.0 x ULN), AST and ALT ≤ 3 x ULN. * Adequate renal function: estimated glomerular filtration rate (eGFR) ≥ 50 mL/min/1.73 m2 (according to CKD-EPI formula). * Adequate coagulation function: INR ≤ 1.5 x ULN (the ULN for INR is defined with the value 1.2 for all sites, in case no ULN is documented in the lab certificates/sheets). In case patient is under anti-vitamin K treatment, INR \>1.5 x ULN is allowed; however, the patient has to be switched to LMWH treatment prior to any trial intervention. * Women of childbearing potential must use effective contraception, are not pregnant or lactating and agree not to become pregnant during trial treatment and until 5 months after the last dose of nivolumab. A negative pregnancy test before inclusion into the trial is required for all women of childbearing potential (for nivolumab product information). * Men agree not to donate sperm or to father a child during trial treatment and until 7 months after the last dose of nivolumab (for nivolumab product information). Exclusion criteria: * Clinically significant ascites that is not controllable. * Prior radiotherapy to any PDAC disease site. * Prior treatment with any immune checkpoint inhibitor. * Concomitant or recent (within 100 days of registration) treatment with any other experimental drug (enrollment in another clinical trial). * Concomitant use of other anti-cancer drugs or radiotherapy. * Severe or uncontrolled concurrent illness, such as cardiovascular disease (congestive heart failure NYHA III or IV; unstable angina pectoris, history of myocardial infarction within the last six months, serious arrhythmias requiring medication (with exception of atrial fibrillation or paroxysmal supraventricular tachycardia), significant QT-prolongation, uncontrolled hypertension. * Known history of human immunodeficiency virus (HIV) or active chronic Hepatitis C or Hepatitis B Virus infection or any uncontrolled active systemic infection requiring intravenous (i.v.) antimicrobial treatment. * Known history of tuberculosis, known history of primary immunodeficiency, known history of allogeneic organ transplant, receipt of live attenuated vaccine within 30 days prior to registration. * Concomitant or prior use of immunosuppressive medication within 30 days of registration, with the exceptions of intranasal and inhaled corticosteroids, or systemic corticosteroids which must not exceed 10 mg/day of prednisone (or a dose equivalent corticosteroid), and the premedication for chemotherapy * Concomitant need for full anticoagulation treatment that cannot be stopped or bridged for the performance of the biopsy/IRE procedures Note: Aspirin or other acetylsalicylic acid containing drugs (up to 300 mg/day) are allowed * Any concomitant drugs contraindicated for use with the trial treatment according to the approved product information * Known hypersensitivity to nivolumab or to any component of nivolumab, to stainless steel or to contrast agents. * Any other serious underlying medical (in particular coagulation deficiencies), psychiatric, psychological, familial or geographical condition, which in the judgment of the investigator may interfere with the planned staging, treatment and follow-up, affect patient compliance or place the patient at high risk from treatment-related complications.