Stages of Cancer: Cancer Basics (Part 2 of 4)

Stages of cancer: TNM staging

Staging is a method of evaluating the progress of cancer in a patient. It plays an important role in deciding the best course of treatment. Let us look at one of the most widely known staging method – TNM staging. In addition, we’ll look at colon cancer (ie, a solid tumour) as an example to understand the Staging nomenclature.

Undertanding the cancer stagging well is important not just for doctors but also for patients and families to understand the names and meanings of stages of cancer. By examining the tumor and the extent to which it has spread to other parts of the body, doctors know how far along the cancer is. It also helps patients and their families ask the right questions and have the right kind of conversation with the oncologist.

Colon Cancer Staging: Dukes Classification

The original Dukes classification system to determine stages of cancer placed patients into one of three categories (Stages A, B,C). Due to few shortcomings this system was subsequently modified by Astler-Coller to include a fourth stage (Stage D) and was further modified by Gunderson & Sosin in 1978. However, very few oncologists/ oncology centres use this classification any more.

TNM Staging (Tumor-Node-Metastasis)

Most noteworthy, the American Joint Committee on Cancer (AJCC) has introduced the TNM staging system to determine the right stages of cancer, which places patients into one of four stages (Stage I–IV). In addition, standardised system has been ratified by the Union for International Cancer Control (UICC) and is now used all over the world.

‘T’ for Tumour:

In the TNM staging, ‘T’ stands for Tumor and describes the extent to which the tumour has penetrated through the walls of the organ to which it is attached. In the colon cancer example:

  • T1: means the tumor has penetrated into the submucosa (the innermost layer of the bowel wall) but has not gone further.
  • T2: means the tumor has penetrated through the submucosa and into the muscularis propria (the muscular and middle layer of the bowel wall)
  • T3: means the tumor has penetrated through the muscularis propria into the subserosa (outermost layer of the bowel wall), or into the pericolic (the outer lining of the colon) or perirectal (outer lining of the rectum) tissues.
  • T4: means the tumor has directly penetrated other organs or tissue structures.

‘N’ for Node:

‘N’ stands for Node (ie, lymph nodes) and describes the extent to which the cancer cells have entered or have spread through the lymphatic system.

  • N0: means there are no cancer cells present in the regional lymph nodes
  • N1: means there are cancer cells present in 1 to 3 regional lymph nodes.
  • N2: means there are cancer cells present in 4 or more regional lymph nodes.

‘M’ for Metastasis:

‘M’ stands for Metastasis and describes the extent to which the cancer cells have spread to other parts of the body – beyond the lymph nodes – and/or have attached themselves to another organ or tissue (for example, the liver, lung or bone).

M0: means no distant metastasis ie, no evidence of cancer cells elsewhere in the body
M1: means distant metastasis present ie, cancer cells (or a secondary tumour) is present elsewhere in the body

To illustrate this through a few examples

  • A T3-N0-M0 classification means the tumour has not breached the outer layer of the bowel wall, there are no tumour cells in the lymph nodes and there is no spread to other organs. Such a classification would merit a positive prognosis
  • A T2-N2-M0 classification means there is evidence of tumour cells in the lymph nodes and even though there is no metastasis, there may be a risk of future spread.
  • In conclusion, a T4-N2-M1 classification means the tumour has breached the bowel wall, there are cells present in the lymph nodes and the cancer has spread to distant organs. Such a classification would merit immediate and perhaps more aggressive treatments.

Stages of cancer: Groupings

While the T-N-M system is very precise, it can be confusing sometimes. In an attempt to simplify, the various T-N-M possibilities have been further grouped into what are called ‘Stages’. Once again, to use the colon cancer example:

Stages of cancer: TNM staging                      Stage I: T1 N0 M0 and T2 N0 M0
Cancer is restricted to the colon and is still within the inner lining.
Stages of cancer: TNM staging Stage II: T3 N0 M0; T4 N0 M0
Cancer has penetrated the outer wall of the colon (or rectum) but it has not reached the lymph nodes or any surrounding organs.
Stages of cancer: TNM staging Stage III: any T, N1-2, M0
Cancer has spread to the lymph nodes, but has not been carried to distant parts of the body.
Stages of cancer: TNM staging Stage IV: any T, any N, M1
Consequently, cancer has metastasized ie, it has been carried through the lymph system to distant parts of the body.

Application for other cancers

Furthermore, note that the T-N-M system applies only to solid tumours and even here, it is used with certain variations

  • With Colon, Breast, Kidney, Lung, Non-Melanoma Skin, Prostate, Testicular and Bladder cancer, the T-N-M system is used, as described above
  • For Cervical and Ovarian cancers, the F-I-G-O (International Federation of Gynaecology and Obstetrics) system has been adopted into the T-N-M system
  • With Liver cancer, the Stage 1-4 system is mostly used
  • For Melanoma, in addition to T-N-M, further Micro-staging is often used
Please ask your oncologist to explain the relevant staging system for you.

Reflection

  • How well have you understood your cancer staging?
  • How would you explain it to someone else: your 12 year old niece, for example?  
  • What relevant questions would you like to ask your doctor about your specific staging?

More from this series

Title About the article
Part 1: The Cell That Forgot To Die Talking openly about cancer is difficult. This is because the cancer experience forces us to confront our own mortality or at least our vulnerability. Hence, that is not something we share so easily.
Part 2: Staging Staging is a method of evaluating the progress of cancer in a patient. Due to examination of the tumor and the extent to which it has spread to other parts of the body, doctors know how far along the cancer is and based on this, decide on the best course of treatment.
Part 3: What Causes Cancer A lot is known about the physical process of cancer. However, it is astonishing how little we know about its physicalcauses. Available research shows that there are two (physical) causes of cancer – tendencies and triggers.
Part 4: Medical Treatments Mainstream (allopathic) cancer treatments include surgery, chemotherapy, radiotherapy and biotherapy.

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