Secondary malignant neoplasm of retroperitoneum and peritoneum

This code signifies the presence of a metastatic cancerous tumor that has spread to the retroperitoneal space or the peritoneum from a primary cancer site elsewhere in the body. It indicates that the malignancy in these locations is not the original cancer but a secondary manifestation.

Use this code when documentation clearly states a malignant neoplasm of the retroperitoneum or peritoneum is metastatic or secondary. This is typically supported by pathology reports confirming malignancy and imaging studies showing tumor involvement in these areas, along with a known primary cancer.

• Always sequence the primary malignant neoplasm first, followed by this code for the secondary site.
• Do not use this code if the retroperitoneal or peritoneal malignancy is identified as the primary cancer; instead, use a code from the 158 series.
• Ensure the documentation explicitly states "secondary," "metastatic," or "spread to" the retroperitoneum or peritoneum.