ICD-10-CM > C00-D49 > C45-C49 > C48 C48 Malignant neoplasm of retroperitoneum and peritoneum Non-Billable/Non-Specific Type 1 Excludes Kaposi's sarcoma of connective tissue (C46.1)mesothelioma (C45.-) Codes C48.0Malignant neoplasm of retroperitoneumC48.1Malignant neoplasm of specified parts of peritoneumC48.2Malignant neoplasm of peritoneum, unspecifiedC48.8Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum