C78.6 Secondary malignant neoplasm of retroperitoneum and peritoneum

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

Applies from C78 Secondary malignant neoplasm of respiratory and digestive organs

Excludes1 (never code together)

• secondary carcinoid tumors of liver (C7B.02)
• secondary carcinoid tumors of peritoneum (C7B.04)

Excludes2 (not included here)

• lymph node metastases (C77.0)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 17 — Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic
• CMS-HCC V22: HCC 8 — Metastatic Cancer and Acute Leukemia
• RxHCC V08: HCC 20 — Lung, Kidney, and Other Cancers; Secondary Cancer of Lymph Nodes and Other Sites
• ESRD V24: HCC 8

MS-DRG index

Defines the logic of DRG(s) 374-376 in MDC 06.

Approximate ICD-9-CM (GEMs)

• 197.6 Secondary malignant neoplasm of retroperitoneum and peritoneum

Code annotations containing back-references to C78.6

Back-references to C78.6

• Code First: R18.0 Malignant ascites ("secondary malignant neoplasm of retroperitoneum and peritoneum (C78.6)")

Diagnosis Index entries for C78.6

• Carcinomatosis › peritonei
• Pseudomyxoma peritonei

Nearby codes

• C78.3 Secondary malignant neoplasm of other and unspecified respiratory organs
• C78.30 Secondary malignant neoplasm of unspecified respiratory organ
• C78.39 Secondary malignant neoplasm of other respiratory organs
• C78.4 Secondary malignant neoplasm of small intestine
• C78.5 Secondary malignant neoplasm of large intestine and rectum
• C78.6 Secondary malignant neoplasm of retroperitoneum and peritoneum (this code)
• C78.7 Secondary malignant neoplasm of liver and intrahepatic bile duct
• C78.8 Secondary malignant neoplasm of other and unspecified digestive organs
• C78.80 Secondary malignant neoplasm of unspecified digestive organ
• C78.89 Secondary malignant neoplasm of other digestive organs