C78.5

HCC Category Mapping

What This Code Means

Cancer that has spread to the large intestine (colon) or rectum from a primary cancer that started in another part of the body.

Coding Tips

• •Document whether the metastasis is to the colon, rectum, or both; this code encompasses the entire large intestine and rectum
• •Code the primary malignancy separately and ensure clinical documentation confirms metastatic rather than primary colorectal cancer

Clinical Significance

Secondary malignant neoplasm of the large intestine and rectum indicates metastatic disease to the colon or rectum from a cancer that originated elsewhere. This is an important distinction from primary colorectal cancer, which is far more common. Proper identification of secondary colorectal malignancy affects staging, treatment approach, and prognosis estimation.

Documentation Requirements

• ✓Primary cancer site must be identified and coded separately
• ✓Documentation confirming metastatic rather than primary colorectal cancer — pathology, imaging, or clinical assessment
• ✓Specific segment of large intestine if documented — ascending, transverse, descending, sigmoid, or rectum
• ✓Whether diagnosed by colonoscopy, imaging, or surgical specimen
• ✓Complications such as obstruction, bleeding, or perforation

Commonly Confused Codes