2.3. Vital Status and Classification of CRC Cases

The unique national identification number given to all Norwegian citizens was used to link NOWAC participants to the population register (Statistics Norway) for vital status (alive, emigrated, dead), and to the Cancer Registry of Norway for cancer incidence.

CRC cases were classified according to the International Classification of Diseases, Seventh Revision (ICD-7) by the Cancer Registry of Norway and further classified according to anatomic subsite: CRC (ICD-7 code 153.0–154.0); colon cancer (ICD-7 code 153.0–153.9); proximal colon cancer (ICD-7 code 153.0–153.1: cecum, ascending and transverse colon including hepatic and splenic flexures); distal colon cancer (ICD-7 code 153.2–153.3: descending and sigmoid colon); and rectal cancer (ICD-7 code 154.0). Cancers of the colon with codes 153.4 (recto-sigmoid junction), 153.6 (appendix), and 153.9 (unspecified location) were only included in the analyses for total colon cancer. Anal canal tumors (ICD-7 code 154.1) were not included in the analyses. Moreover, only cases with ICD-O tumor behavior code 3 (malignant, primary cite) were classified as CRC.