Additional Study Information: The purpose of this study is to find out which doses of talimogene laherparepvec (T-Vec) can be given safely to patients with pancreatic cancer that is either too big to be taken out by surgery or has spread to other parts of the body. The study will also see if T-Vec can cause tumor shrinkage or prevent its growth. To find out which doses are safe, all subjects enrolled in this study will receive up to 4 injections of T-Vec. At least two doses will be evaluated in this study, depending on how many side effects are seen at each dose. You will not be able to pick your dose, as this will be determined based on the study experience with subjects enrolled before you. T-Vec is called a study agent in this form. The use of T-Vec in pancreatic cancer is still experimental and has not been approved by any regulatory health agency (like the Food and Drug Administration FDA or European Medicines Agency EMA) for use in people with pancreatic cancer. T-Vec however has been approved by the FDA for use in melanoma patients.