Effects of Cold Atmospheric Plasma (CAP) on Peritoneal Tumor Tissue

* Surgery and application of CAP: at the start of surgery, an inventory is made of suitable tumor nodules that will be planned for resection. Nodules should have a maximal size of 2-3 mm, since it is unlikely that bigger lesions can be adequately treated with CAP. * Selected tumor nodules will be treated with the J-plasma device at the standard settings (Helium gas flow of 4 l/min, coagulation and cutting intensity at 35). The distance between the tip of the device and the tissue will be approx. 10 mm. Using a timer and footswitch, nodules will be treated at different power settings and durations: * 15 W, 30W, or 45W * 2, 5, or 10 seconds. * The treated nodules will be resected at least 30 minutes after plasma treatment, and the exact timing will be documented. The samples are split in half: one half is fixed in formalin for histology and immune histochemistry, and the other half is immediately processed for live/death staining using flow cytometry.