International Classification of Diseases, 4th Edition (ICD-O-4)

It is almost time for a new International Classification of Diseases for Oncology! The International Association of Cancer Registries (IACR) has announced it is moving forward with new morphology codes and a new morphology code structure in its International Classification of Diseases for Oncology, 4^th Edition (ICD-O-4). This new structure uses five digits and enables the assigning of specific codes to cancers that were previously included in “related terms,” and the addition of new terms. In many scenarios the 5^th digit will be ‘0’; however, the format is alphanumeric so some will include alpha characters. The ICD-O-4 topography list will also be updated. An ICD-O-4 draft has been released for comment with feedback to be submitted by November 1, 2024.

The NAACCR ICD-O Work Group will review the ICD-O-4 draft to provide feedback. Each of the standard setting organizations are represented on the ICD-O WG as well as central registries and software vendors. Initial review by the ICD-O Work Group will include, but not limited to, looking at changes that will impact cancer surveillance, behavior code changes, terms with a code for a long time that have changed, deleted codes, new histology terms added by the World Health Organization (WHO) that are not in the 5^th Edition WHO blue books, and inconsistent use of NOS (not otherwise specified).

The Mid-Level Tactical Group (MLTG) will assess the impact of the ICD-O-4 implementation and submit a recommendation for an implementation timeline to the High-Level Strategic Group (HLSG). The transition to ICD-O-4 will affect many areas of the cancer registry community, their processes, software, trends, etc. The MLTG, which is made up of all North American cancer registry standard-setters (AJCC, CCCP, CoC, NAACCR, NPCR, and SEER) as well as CAP and NCRA, will manage and coordinate the implementation process to ensure a smooth transition.

Don’t panic! We have been there, done that! ICD-O has been the standard for collection of primary site and morphology by cancer registries for more than 50 years. Some of us can remember going from ICD-O-1 to ICD-O-2 and then from ICD-O-2 to ICD-O-3. Our community has experienced these types of changes before, and we have managed our way through the challenges. As we know, change is inevitable in our field. The cancer surveillance community is comprised of strong leadership and subject-matter experts that will continue to guide us through change.

Stay tuned as we navigate through the comment period, discuss the implementation impacts, develop an implementation plan, and continue to move our field forward.