Download the Solid Tumor Rules 2026 Update (PDF, 8.7 MB) (December 12, 2025)

Purpose of Solid Tumor Rules

The purpose of the Solid Tumor Rules is to determine the number of primaries to abstract and the histology to code. The most recent Solid Tumor Rules update should be used as soon as it is released and can be applied to 2018+ cases (see General Instructions for start years for each Site-group). If a specific code or instruction has an effective year later than 2018, it will be noted in the text.

2026 Solid Tumor Rules Release Announcement

The Solid Tumor Rules have been updated for 2026. In addition to the standard annual updates, the Solid Tumor Manual underwent a substantial reformatting to improve clarity and usability.

Key updates include the following:

  • Restructured general instructions
  • Reformatted and restructured the histology tables
    • Changed from 3 columns to 2 columns
    • Histology corrections made in several site-group tables
    • In-table notes moved to footnotes
  • Malignant and Non-malignant CNS: Table 1: WHO Grades for Select CNS Neoplasms has been replaced by a link to the most current CAP Protocol for CNS.
  • Updated list of ambiguous terms that can be used for determining histology
  • Breast rules M10 and H28 deleted

See the Revision History for a comprehensive description of changes.

NOTE: For information on implementation of the 2026 update, see the Diagnosis Years for Which the Solid Tumor Rules Should Be Used section in the General Instructions (page 7).

Educational Opportunities

The 2026 updates to the Solid Tumor Manual will be discussed during the V26 Updates: Solid Tumor Rules, SSDIs, CPC and MoreExternal Web Site Policy informational webinar on January 14, 2026 at 2pm ET. Registration is free and participants are eligible for 2 continuing education (CE) credits.

A more in-depth discussion of the changes will be included in the SEER 2025-2026 Advanced Topics for Registry Professionals on Demand Workshop.

Where Should I Submit Questions?

Questions concerning the Solid Tumor Rules Manual can be directed to the Ask A SEER Registrar Forum.

Revision History

Significant formatting changes were made to the histology tables. Please see the 2026 Update Revisions. Changes for earlier versions are available in the Revision Archive.

Suggested Citation

Dickie, L., Adams, S., Harrison, D., Hofferkamp, J., Traverso-Ortiz, M., Van Dyke, A., Negoita, S. (December 2025). Solid Tumor Rules. National Cancer Institute, Rockville, MD 20850.