How Is the Stage of Lung Cancer Determined?

The American Joint Committee on Cancer (AJCC) created the TNM scoring system to describe different phases of cancer growth, where:

• T = Tumor size and invasiveness into adjacent tissues
• N = Lymph Node involvement, in particular the nearby lymph nodes
• M – Metastasis, or spread of the cancer, to distant sites

The TNM staging system is the most widely used cancer staging system and is commonly used by hospitals, medical centers, and in clinical trials.^1,2

Understanding the TNM scoring system

The first measure of the TNM system is the tumor size and extent. This is based on the primary tumor – the location the cancer began. The T scores for lung cancer are:

• TX – The main tumor is too small for testing or cannot be assessed; cancer cells may have been seen on sputum cytology (looking at mucus through a microscope) or bronchial washing (flushing the lungs for lung cell samples).

• T0 – There is no evidence of a primary tumor.

• Tis – Abnormal cells in the bronchi (air tubes) are present but it hasn’t invaded deeper into lung tissue. This stage of cancer is also known as carcinoma in situ.

• T1 – The tumor is in the lung only and not larger than 3 cm.
  • T1a – The tumor is 2 cm or smaller.
  • T1b – The tumor is more than 2 cm but not larger than 3 cm.

• T2 – The tumor is larger than 3 cm but not larger than 7 cm or has additional features, including involving a main bronchus, grown into the surrounding membrane (visceral pleura), or the tumor partially clogs the airways.
  • T2a – The tumor is larger than 3 cm but not larger than 5 cm with or without other features, or it is smaller in size but has other features.
  • T2b – The tumor is larger than 5 cm but not larger than 7 cm with or without other features.

• T3 – The tumor has one or more of the following features: is larger than 7 cm; has grown into the bronchus within 2 cm of the carina (the point at which the windpipe splits into the right and left bronchi); has grown into the parietal plura (membrane around the chest cavity), chest wall, diaphragm, phrenic nerve (nerve that starts in the neck and runs down through the chest), mediastinal pleura (membrane between the lungs), or outer pericardium (membrane around the heart); has caused the lung to collapse or caused inflammation of the whole lung; or there are additional tumors in the same lobe with the primary tumor.

• T4 – The tumor has one or more of the following features: has grown into the mediastinum (the space between the lungs), the heart, the large blood vessels near the heart, the windpipe (trachea), the esophagus, the backbone, or the carina; additional separate tumor nodules are present in different lobes of the same lung.^1,3

Measuring lymph node involvement

The second measure of the TNM system is for lymph node involvement. Cancer cells can spread through the lymph system.

• N0 – No cancer is evident in nearby lymph nodes.
• N1 – The cancer has spread to the peribronchial nodes in the lungs and/or to the hilar nodes (found just outside the lungs) and the intrapulmonary nodes (found inside the lungs) in the same lung as the primary tumor.
• N2 – The cancer has spread to mediastinal nodes (found in the center of the chest), which include the subcarinal nodes (found just underneath the carina).
• N3 – The cancer has spread to the mediastinal or hilar nodes near the lung without the primary tumor, or to any supraclavicular (above the collarbone) or scalene (in the neck) lymph nodes.¹

Noting cancer metastases

The third measure of the TNM system notes metastases, places where the cancer has spread to distant parts of the body.

• M0 – The cancer has not spread to distant sites.
• M1 – The cancer has spread to distant sites.
  • M1a – The cancer has spread: from one lung to the other lung; into the lung’s lining (pleura) and has formed secondary tumors; or into the fluid around the lungs or the heart.
  • M1b – The cancer has spread to areas outside the chest area. Lung cancer tends to spread to the brain, adrenal gland (located above the kidneys), liver, or bones.^1,3

Lung cancer stages

The AJCC has created the following stages of cancer based on the TNM numbers.^1,4

About the AJCC

The AJCC has a mission to provide worldwide leadership in the development, promotion, and maintenance of evidence-based systems for the classification and management of cancer in collaboration with multidisciplinary organizations dedicated to cancer surveillance and to improving care. The AJCC established the way cancer is communicated by creating the TNM system, the Cancer Staging Manual, and the Cancer Staging Atlas. Publications by the AJCC are used by thousands of medical professionals and are recognized as the authoritative guides for cancer staging information.⁴