Retroperitoneum and Peritoneum

T-C48 designates malignant neoplasms that arise in the retroperitoneum or the peritoneal lining, encompassing primary cancers of the peritoneum, retroperitoneal soft-tissue sarcomas, and other tumors originating in these deep abdominal compartments. The code is used to classify tumors whose primary site is the space behind the peritoneum or the peritoneal cavity itself, distinguishing them from intra-abdominal organ cancers.