TNM Staging System in Cancer Diagnosis

TNM Staging System

• The TNM staging system uses three descriptors: T for primary tumor, N for lymph node involvement, and M for metastasis.

Primary Tumor (T)

• TX: Primary tumor cannot be assessed
• T0: No evidence of primary tumor
• Tis: Carcinoma in situ (intraepithelial or intramucosal)
• T1: Tumor invades submucosa (through the muscularis mucosa)
• T2: Tumor invades muscularis propria
• T3: Tumor invades pericolorectal tissues
• T4: Tumor invades visceral peritoneum or adheres to adjacent organ or structure
• T4a: Tumor invades through the visceral peritoneum (including gross perforation of the bowel through tumor)
• T4b: Tumor directly invades or adheres to other organs or structures

Regional Lymph Nodes (N)

• NX: Regional lymph nodes cannot be assessed
• N0: No regional lymph node metastasis
• N1: Metastasis in 1-3 regional lymph nodes
• N1a: Metastasis in 1 regional lymph node
• N1b: Metastasis in 2-3 regional lymph nodes
• N1c: Tumor deposit(s) in the subserosa, mesentery, or nonperitonealized pericolorectal tissues without regional nodal metastasis
• N2: Metastasis in 4 or more lymph nodes
• N2a: Metastasis in 4-6 regional lymph nodes
• N2b: Metastasis in 7 or more regional lymph nodes
• N Suffix:
  • (sn): Select if regional lymph node metastasis identified by sentinel lymph node biopsy only
  • (f): Select if regional lymph node metastasis identified by fine needle aspiration biopsy only

Prognostic Factors

• Bowel obstruction at diagnosis is associated with worse prognosis
• Ulcerative growth pattern is associated with worse prognosis
• Perforation is associated with worse prognosis
• Elevated preoperative CEA level is associated with worse prognosis

Approach Considerations

• Surgery is the only curative modality for localized colon cancer (stage I-III)
• Linitis plastica has an extremely poor prognosis

Clinical Staging

• Stage 0: Tis, N0, M0
• Stage I: T1-2, N0, M0
• Stage IIA: T1-2, N1-3, M0
• Stage IIB: T3, N0, M0 or T4a, N0, M0
• Stage III: T3, N0, M0 or T4a, N1-3, M0
• Stage IVA: T4b, any N, M0
• Stage IVB: Any T, any N, M1

Survival Rates

• Stage IA: 94%
• Stage IB: 88%
• Stage IIA: 82%
• Stage IIB: 68%
• Stage IIIA: 54%
• Stage IIIB: 36%
• Stage IIIC: 18%
• Stage IV: 5%

Spread Patterns

• Direct extension into omenta, pancreas, diaphragm, transverse colon or mesocolon, and duodenum is common
• Peritoneal involvement is frequent if the lesion extends beyond the gastric wall to a free peritoneal surface
• The visible gross lesion frequently underestimates the true extent of the disease
• Abundant lymphatic channels within the submucosal and subserosal layers of the gastric wall allow for easy microscopic spread

Laboratory Studies

• The goal is to assist in determining optimal therapy
• Malignant or inflammatory lymph nodes detected on EUS have characteristic features:
  • Enlarged in size
  • Hypoechoic (dark)
  • Homogeneous
  • Well circumscribed and rounded

Bronchoscopy

• Indicated for cancers of the middle and upper third of the thoracic esophagus to help exclude invasion of the trachea or bronchi
• Laparoscopy and thoracoscopy have a greater than 92% accuracy in staging regional nodes

Barium Swallow

• Very sensitive for detecting strictures and intraluminal masses
• Does not allow staging and biopsy
• May be helpful for studying the distal anatomy in obstructive tumors inaccessible by endoscopy