TNM Classification and Cancer Staging Simplified

You must be asking yourself – “how to remember the TNM staging system?” and looking here and there for mnemonics only to find nowhere. Understanding the oncoanatomy helps to understand the staging system of the cancers.

Tumor Status (T)

Size of T1 in various tumors

Head and neck, Parotid, Thyroid, Breast, Liver, Pancreas, Anus, Skin: ≤ 2 cm

• 2-5 cm is T2 in breast carcinoma and >5 cm is T3 and extension to chest wall is T4.
• 2-4 cm is T2 in head and neck cancers including thyroid and >4 cm is T3 and invasion of adjacent structures is T4.
• >5 cm (atleast 1 of the multiple nodes) is T3 in liver as well but T2 is <5 cm with multiple nodes or requires vascular invasion.
  • T4 is invasion of adjacent structures other than gallbladder or with visceral peritoneum.

Lungs: ≤ 3 cm

• 3-7 cm is T2 in lung cancer and >7 cm is T3.

Cervix: < 4 cm

• >4 cm is T1b2.

Soft tissue sarcomas: ≤ 5 cm

• >5 cm is T2.
• There are no T3 and T4.

Kidney: ≤ 7 cm

• >7 cm is T2.
• Local invasion within Gerota’s fascia (including adrenal glands and IVC) is T3.
• Invasion beyond Gerota’s fascia is T4.

Bone: < 8 cm

• >8 cm is T2
• Skip lesions at primary site is T3
• There is no T4

Nodal Status (N)

Lymph node sizes

Head and neck tumors:

3 Nodal stages 3 cm increment in sizes

• N1: ≤3 cm
• N2: 3-6 cm
• N3: >6 cm

Genitourinary tumors (only Testes and Renal pelvis):

• N1: ≤2 cm
• N2: 2-5 cm
• N3: >5 cm

Lymph node numbers

Head and neck cancers, Urinary Bladder Cancer:

• N1: Solitary node
• N2: Multiple nodes

Colorectal carcinoma:

• N1: 1-3
• N2: ≥4

Gastric carcinoma:

• N1: 1-2
• N2: 3-6
• N3: >6 (a – 7 to 15; b – >15)

General Idea for Staging According to TNM classification

Correlation between the Tumor stage (T) and ease of nodal (N) involvement based on whether the regional lymph node basin is within or outside the capsule or serosa gives an idea about staging the malignancy.

When regional lymph nodes are within the capsule or serosa: T1 or T2 = N1

• Lung: N1 (hilum and other intrapulmonary nodes) are within pleura
• Breast: N1 (Level I and II axillary) and N2 (internal mammary nodes) are adjacent to breast tissue (also extensive subcutaneous lymphatics)
• Stomach: Lymph nodes in Muscularis propria (Beyond serosa in other GI tracts)
• Penis and urethra: Rich subcutaneous lymphatics drain to juxtaposed femoral nodes at the crura of penis without a capsule.

When regional lymph nodes are beyond the capsule: T3=N1

• Pancreas
• Gallbladder
• Kidney
• Ovary
• Fallopian tube
• Uterine fundus
• Cervix
• Vagina and Vulva

When regional lymph nodes are beyond the serosa in hollow organs: T4=N1

• Colon
• Rectum
• Urinary bladder
• Renal pelvis
• Testis

Esophagus has a thin adventitia, and therefore, T3=N1.

When regional lymph nodes are distant to primary sites: T4=N1

• Skin cancer
• Melanoma
• Merkel cell cancer
• Soft tissue and bone sarcomas

Separate Stage

Testicular cancers

• M1a = Non-regional nodes metastases = stage III
• M1b = Lungs metastases = stage IV

Trophoblastic tumors

• M1a = Lung metastases = stage III
• All other distant metastases = stage IV

Hematologic malignancies

Most hematologic malignancies have separate staging system, example – Ann Arbor Staging for Hodgkin’s Lymphoma.

Source: TNM Staging Atlas with Oncoanatomy 2nd edition By Philip Rubin, John T. Hansen