Q&A: Using the TNM staging system for coding cancer

Q: I recently heard in a class that the TNM (tumor, nodes, metastasis) system can be used for coding purposes, but I’ve never used it before. As a coding professional, should I know how this system works and how to apply it?

A: To begin, let’s go over the TNM staging system. The TNM staging system is the most widely used cancer staging system and is therefore often used by physicians. According to the National Cancer Institute, most hospitals and medical centers use it as the main method for cancer reporting. In the TNM staging system:

• T refers to the size and extent of the main or primary tumor
• N refers to the number of nearby lymph nodes that have cancer
• M refers to whether the cancer has metastasized

When a physician uses this system, they assign numbers after each of the letters in the TNM system:

• T (primary or main tumor):
  
  • TX: Main tumor cannot be measured
  • T0: Main tumor cannot be found
  • T1, T2, T3, T4: Refers to the size and/or extent of the main tumor. The higher the number after the T, the larger the tumor or the more it has grown into nearby tissues. Ts can be further divided for more detail, such as T3a, etc.
• N (nearby lymph nodes):
  
  • NX: Cancer in nearby lymph nodes cannot be measured
  • N0: There is no cancer in nearby lymph nodes
  • N1, N2, N3: Refers to the number and location of lymph nodes that contain cancer. The higher the number after the N, the more lymph nodes that are affected.
• M (metastasis):
  
  • MX: Metastasis cannot be measured
  • M0: Cancer has not spread to other parts of the body
  • M1: Cancer has spread to other parts of the body

As far as using this system for coding purposes, take a look at AHA Coding Clinic, First Quarter 2014, p. 12, which specifies that codes can be assigned based on documentation using the TNM staging system when authenticated by the staging physician.

As a coding professional, it’s helpful to learn the TNM system so that, if a provider uses the system in his or her documentation, you can correctly interpret that information and assign the appropriate code or identify an opportunity to query for further information based on the direction of the Coding Clinic mentioned above.

For example, if the provider documents “carcinoma of the cervix—T4N1M0,” you would apply this knowledge to understand that there is a large tumor in the cervix, as explained by the T4, that has spread to the lymph nodes as explained by N1, and that there is no distant metastases as explained by the M0.

The documentation of N1 per this Coding Clinic will allow you to assign the C77.5 code identifying unspecified neoplasm of the intrapelvic lymph nodes.

If the documentation stated M1- you would also be able to assign the appropriate code for metastatic disease. You would likely need to query to further specify the location of the metastases.  

Editor’s Note: Laurie L. Prescott, RN, MSN, CCDS, CDIP, CRC, CDI education director at HCPro in Middleton, Massachusetts, answered this question. Contact her at lprescott@hcpro.com. For information regarding CDI Boot Camps, click here.