Staging of Colorectal Cancer

Introduction to Staging

The American Joint Committee on Cancer (AJCC) recommends using the TNM system to stage colorectal cancer, which evaluates the depth of tumor penetration (T), the status of lymph nodes (N), and the presence of distant metastasis (M) 1, 2

The TNM system uses a dual classification that includes clinical classification (cTNM) for pre-treatment evaluation and pathological classification (pTNM) for post-surgical histopathological evaluation to determine prognosis 1, 2

Stage 0: Tis N0 M0 (carcinoma in situ) 1, 2
Stage I: T1 N0 M0 or T2 N0 M0, equivalent to Dukes A, with a 5-year survival rate of 93.2% 1, 2, 3
Stage II:
Stage III:
Stage IV: Any T, any N, M1, with a 5-year survival rate of 8.1% 1, 2, 3

Initial clinical evaluation requires a complete medical history, physical examination, laboratory tests (including CEA and liver function tests), and a complete colonoscopy or proctosigmoidoscopy with air-contrast barium enema 1, 2, 5
Surgical and pathological staging evaluates metastasis to the liver, lymph node dissemination, tumor extension through the intestinal wall, and resection margins (R0, R1, R2) 1, 3, 4
A minimum of 12-14 lymph nodes must be evaluated for accurate staging of stage II colorectal cancer 1, 3, 5

Histological grade, lymphatic, venous, or perineural invasion, intestinal obstruction or perforation, preoperative elevated CEA or CA19-9 levels, and lymphoid inflammatory response are important prognostic factors beyond the TNM system 1, 2, 5, 7

Inadequate lymph node extraction (<12 nodes) can lead to under-staging and inappropriate therapeutic decisions 5, 8
The prognosis of stage II improves significantly when 12-14 lymph nodes are removed, although it is unclear whether this is a surgical or pathological issue 1, 2
Locoregional imaging staging is not routine for colorectal cancer (unlike rectal cancer), but CT is still recommended for global evaluation and detection of complications 6, 9
PET is not recommended for initial staging 5