Data Last Updated: Dec. 17, 2025

Schema Discriminator 1: Primary Peritoneum Tumor

This input is used for staging

Description

The GIST chapter includes a schema discriminator for C481 for location of the primary tumor because all the peritoneum structures are coded to C481, but two separate stage tables are used to derive the TNM values.

Rationale

A schema discriminator is used to assign AJCC ID when site and histology alone are insufficient to identify the applicable AJCC staging method and to assign Schema ID, which links each case to the appropriate SSDIs, Grade, Summary Stage and EOD data collection system.

Additional Info

**Source documents:** pathology report, imaging, physician documentation, physician staging

Notes

**Note:** **Schema discriminator for C481** * Since both omental and peritoneal gastrointestinal stromal tumors (GIST) are coded with the same ICD-O-3 topography code (C481), this data item must be used to identify the appropriate AJCC stage table.
Code Description Stage Table
1 Mesentery
Mesoappendix
Mesocolon
Pelvic peritoneum
Rectouterine pouch
- Cul de sac
- Pouch of Douglas

Other specified peritoneal site		 Small Intestinal, Esophageal, Colorectal, Mesenteric and Peritoneal GIST
2 Omentum Gastric and Omental GIST
9 Unknown or no information
Not documented in medical record		 Small Intestinal, Esophageal, Colorectal, Mesenteric and Peritoneal GIST
<BLANK> Primary Site is NOT C481, Discriminator is not necessary