Malignant neoplasms of retroperitoneum

**Definition:** A primary or metastatic malignant neoplasm [primary malignant neoplasm spreading elsewhere] involving the retroperitoneum. The vast majority of cases are carcinomas, lymphomas, or sarcomas.

**Exclusions:** - Malignant neoplasm metastasis in retroperitoneum - Malignant mesenchymal neoplasms - Malignant neoplasms of omentum - Malignant neoplasms of peritoneum