The peritoneum is your internal skin lining. It coats all the intestines and other organs like the spleen, liver and gallbladder, as well as the gynecologic organs. Some cancers grow on the peritoneum, but arise from other organs, like ovarian cancer. Rarely, cancer can arise in the peritoneal lining itself, and that is called primary peritoneal cancer. That type of cancer is treated just like ovarian cancer. This is different from mesothelioma, which arises from specialized cells in your abdomen or chest, and is treated very differently in terms of the type of chemotherapy.