Definition of Primary Site

Site of origin

Figure 1. Drawing of a skeleton of a young girl. The human skeleton. The skeleton is the framework of bones and cartilage that supports and protects the soft tissues and the internal organs of the body. Source: Terese Winslow (Illustrator), National Cancer Institute

The term “primary site” is defined as the tumor’s site of origin, or where the tumor originated.

The code assigned for primary site should represent the site in which the primary tumor originated, even if the tumor extends onto/into an adjacent subsite. Site of origin may be indicated by terms such as "tumor arose from…," "tumor originated in…," or similar statements. Site of origin is not necessarily the site of a biopsy.

Tumors may involve many sites. The primary site code should reflect the site where the tumor arose rather than all of the sites of involvement.

Under certain circumstances, the primary site originally collected on an abstract should be changed or modified.

• Consults from specialty labs, pathology report addenda or comments, or other information have been added to the chart. Reports done during the diagnostic workup and placed on the chart after the registrar abstracted the case may contain valuable information. Whenever these later reports give better information about the histology, grade of tumor, primary site, etc., change the codes to reflect the better information.
• The primary site was recorded as unknown at the time of diagnosis. At a later date, the physician determines that the cancer arose from a specified primary site.

Updated: December 13, 2023