ICD-10-CM code C78.6 is a critical diagnosis code in the medical field, specifically used to classify Secondary Malignant Neoplasm of Retroperitoneum and Peritoneum. This code is essential for accurate medical billing, statistical tracking, and patient record management within the healthcare system in the United States and other countries adopting the ICD-10-CM system. Effective from October 1, 2024, the 2025 edition of ICD-10-CM C78.6 remains a billable and specific code, indicating its validity for use in reimbursement claims.
In simpler terms, C78.6 signifies cancer that has spread (metastasized) to the retroperitoneum and peritoneum from a primary cancer located elsewhere in the body. The retroperitoneum is the anatomical space behind the abdominal cavity, while the peritoneum is the lining of the abdominal cavity. Understanding this distinction is crucial for precise diagnosis and treatment planning.
Several terms are used synonymously with C78.6, providing different ways to describe the same condition. These approximate synonyms include:
- Cancer metastatic to omentum
- Cancer metastatic to peritoneum
- Cancer metastatic to retroperitoneum
- Cancer of the ovary with peritoneal metastases
- Cancer, carcinomatosis of peritoneal cavity
- Carcinomatosis of peritoneal cavity
- Ovarian cancer metastatic to peritoneum
- Pseudomyxoma peritonei
- Secondary malignant neoplasm of peritoneum
- Secondary malignant neoplasm of retroperitoneum
- Secondary malignant neoplasm of the omentum
- Secondary malignant neoplasm of the peritoneum
The inclusion of terms like “carcinomatosis of peritoneal cavity” and “pseudomyxoma peritonei” highlights the range of conditions that may fall under the C78.6 Diagnosis when the malignancy is secondary. Notably, “Ovarian cancer metastatic to peritoneum” is also listed, indicating that while ovarian cancer can be a primary cancer, its spread to the peritoneum is classified under C78.6 as a secondary malignancy.
From a coding history perspective, C78.6 was introduced as a new code in 2016, marking the first year of the non-draft ICD-10-CM system. Since then, through the 2025 edition, the code has remained unchanged, reflecting its established and consistent use in medical classification.
Within the broader context of ICD-10-CM, C78.6 is positioned amongst related codes concerning secondary malignancies of respiratory and digestive organs. Codes adjacent to C78.6 provide a clearer picture of its place within the classification system:
- C78.00-C78.02: Secondary malignant neoplasms of the lung (unspecified, right, left)
- C78.1: Secondary malignant neoplasm of mediastinum
- C78.2: Secondary malignant neoplasm of pleura
- C78.3-C78.39: Secondary malignant neoplasms of other respiratory organs
- C78.4: Secondary malignant neoplasm of small intestine
- C78.5: Secondary malignant neoplasm of large intestine and rectum
- C78.7: Secondary malignant neoplasm of liver and intrahepatic bile duct
- C78.8-C78.89: Secondary malignant neoplasms of other digestive organs
This list demonstrates that C78.6 is part of a larger category addressing secondary cancers in the respiratory and digestive systems, specifically focusing on the retroperitoneum and peritoneum.
For reimbursement purposes, the use of ICD-10-CM codes, including C78.6, has been mandatory for claims with a date of service on or after October 1, 2015. This underscores the importance of using the correct and most specific ICD-10-CM code for accurate billing and healthcare administration. Understanding the nuances of codes like C78.6 is therefore crucial for healthcare professionals involved in diagnosis, treatment, and medical coding.
