This is a clinical study investigating the new treatment of surgery combined with intraperitoneal mitomycin-C for patients with gastrointestinal cancer that has spread to the peritoneal (abdominal cavity) surface. Mitomycin-C to be used in this procedure is approved by the U.S. Food and Drug Administration (FDA)for many different cancers including gastrointestinal cancer. Giving mitomycin C via the intraperitoneal route is not FDA approved and is an investigation therapy. Cytoreductive surgery plus intraperitoneal chemotherapy can be offered as standard of care outside of a clinical trial. However, since this is an unproven and potentially more effective but a more toxic approach, the investigators are performing this procedure under an IRB approved clinical trial in order to better evaluate the risks and benefits of this approach.