Primary Care Coding Alert

Question: Is it possible to code a secondary neoplasm as primary, or is a primary diagnosis always coded as such?

California Subscriber

Answer: While it may sound confusing, from a coding perspective, sometimes a secondary neoplasm (where the cancer has spread to, or metastasized) can be coded as a primary (principal or first-listed) diagnosis.

Here’s why: When a treatment targets a cancerous condition, that condition is considered the main or primary diagnosis. This means that if the treatment is aimed at a secondary cancer, the secondary cancer becomes the primary diagnosis for that medical encounter.

Example: A patient has colon cancer that has spread to the liver . In this example, the patient still has colon cancer, but the primary (principal or first-listed) diagnosis code for the encounter is metastatic, or secondary, liver cancer, not the colon cancer.

So, you would not code the colon cancer, C18.9 (Malignant neoplasm of colon, unspecified), first, as that is not what is being treated at this encounter. Neither would you code C22.8 (Malignant neoplasm of liver, primary, unspecified as to type) because the liver cancer being treated is not the primary cancer. You also should not report C78.5 (Secondary malignant neoplasm of large intestine and rectum) because colon cancer was not the secondary cancer; the liver cancer was metastatic (secondary cancer) to the colon (primary cancer). Instead, as the treatment is directed to the liver, you will use C78.7 (Secondary malignant neoplasm of liver and intrahepatic bile duct) as the principal, or first-listed, diagnosis for this encounter.

Documentation alert: For metastatic cancers, always closely scrutinize your provider’s documentation. If you see in the notes that the cancer is “metastatic to”, that means the “to” cancer is secondary. If the note reads “metastatic from”, that means the “from” cancer is primary. But for coding purposes, the principal, or first-listed, diagnosis will be the cancer for which the patient is receiving treatment, whether that be a primary or metastatic cancer.