Introduction to the Extent of Disease (EOD) 2018 Data Collection System

To study cancer data, there must be standard ways of describing cancer and the stage at which they are diagnosed and treated. EOD is a standardized coding system developed and used by SEER to share and study cancer data.

EOD is not a staging system.

EOD uses all information available in the medical record; in other words, it is a combination of the most precise clinical and pathological documentation of the extent of disease.

The EOD 2018 coding system consists of three main data items, referred to as building blocks, and is collected for every site and histology combination. (Note: Not every combination of primary site and histology is eligible for deriving a T, N, M, or TNM Stage Group though). The eligibility for deriving T, N, M or TNM Stage Group is based on the current edition of the AJCC manual.

• EOD Primary Tumor (3-digit code)
• EOD Regional Nodes (3-digit code)
• EOD Mets (2-digit code)

The computer algorithm is designed to generate the corresponding stage, based on AJCC 8th edition, from the EOD coded fields, using primary site code, histology code specific schemes based on ICD-O-3, regional nodes positive (schema specific), tumor size (schema specific), and site-specific data items (SSDIs), as needed.

• EOD 2018 T
• EOD 2018 N
• EOD 2018 M
• EOD 2018 Stage Group
• EOD Summary Stage 2018

These data items derive a TNM 8th Stage Group.

• Note: EOD does not derive an AJCC 8th edition stage group. EOD derives a combined clinical/pathological stage, while AJCC has separate stages for clinical and pathological
• Summary Stage 2018 will be derived for all cases (eligibility for AJCC staging does not matter)

The same computer algorithms are used at both the hospital registry and the central registry to derive the stage from the EOD data elements.

Updated: December 11, 2023