The TNM staging system explained

The TNM system (Tumour, Nodes, Metastasis), developed by the American Joint Committee on Cancer, is the most common way to describe the stages for lung cancer, including small cell carcinoma and squamous cell carcinoma. Doctors use the TNM system for non-small cell lung and small cell lung cancer NSCLC to provide a detailed picture of the disease.

T – Tumour

“T” describes the size of the primary tumour and how far it has penetrated lung tissue or into deeper lung tissues. The stage assesses whether the tumour remains within the top lining, the same lobe, or has involved multiple areas of the same lung or more than one tumour.

• T1: Single tumour, small (3 cm or less), found in one lung tissue region.
• T2: Tumour measuring between 3–5 cm or spreading into the bronchus or nearby structures of the chest.
• T3: Tumours (5–7 cm) that affect nearby organs or more than one tumour in the same lung, but on the same side.
• T4: Tumours larger than 7 cm, in both lungs or invading vital organs like the heart, trachea, or other nearby structures.

N – Nodes

“N” assesses whether cancer cells have moved to lymph nodes, including nearby lymph nodes, mediastinal lymph nodes, and whether cancer has spread to the same side or opposite side of the chest.

• N0: No spread to lymph nodes.
• N1: Cancerous cells in lymph nodes on the same side as the tumour.
• N2: Cancer present in lymph nodes further into the centre of the chest.
• N3: Lymph node involvement near the collarbone or on the opposite chest side.

M – Metastasis

The “M” in TNM describes whether the cancer has metastasised to distant organs, such as the brain, liver, adrenal glands, or other lungs.

• M0: No cancer spread to other organs.
• M1: Cancer has spread to distant organs or areas, indicating advanced disease or stage IV.

Understanding the number staging system

The TNM details are often grouped into numbered stages to make it easier for patients and families to understand their cancer’s stage and what each level may mean for their lung cancer treatment journey.

Stage 1 – Localised

• Cancer is within one lung and has not spread to lymph nodes or distant organs; most common type at early stages.
• Early-stage lung cancer offers highly effective treatment options, often with surgery for some lung cancer.

Stage 2 – Regional spread

• The tumour may be larger, and cancer has spread to nearby lymph nodes, but within the same side of the chest or lung.
• Lung cancer stage II often means that surgery may be combined with chemotherapy or other treatments for the best results.

Stage 3 – Locally advanced

• Tumour involves more than one structure or lymph node group, typically in the same lung, deeper lung tissues, or extending to the chest wall.
• Treatment usually requires multiple approaches: chemotherapy, surgery, radiation therapy, or even immunotherapy.

Stage 4 – Metastatic

• Cancer has spread to distant organs (like the brain, liver, adrenal glands), the other lung, or elsewhere in the body.
• Lung cancer cases at this stage often focus on controlling the disease, improving survival rates, and maintaining comfort through various treatment options.

In small cell lung cancer, doctors often use two stages: limited stage (cancer confined to one lung and possibly nearby lymph nodes) and extensive stage (spread beyond the original lung or to other organs).

Clinical vs. pathologic staging

Staging for lung cancer involves both clinical stage (before treatment) and pathologic stage (after surgery or more detailed tissue analysis).

Clinical staging

• Performed before treatment, using physical exams, imaging tests, and sometimes other tests to estimate the cancer’s stage.
• Helps doctors plan the first steps in your lung cancer treatment, identifying the presence of tumour, whether cancer cells are in the same lung or elsewhere, and if surgery is possible.

Pathologic staging (surgical staging)

• Determined after surgery or tissue sample analysis, the examination of the tumour, lymph nodes, and other relevant tissues.
• Often more accurate as it looks at actual cancerous cells and spread, not just imaging or clinical impressions.

Grading lung cancer

Grading focuses on the appearance of cancer cells compared to normal cells found in lung tissues. Doctors look at how well-differentiated or poorly differentiated the cells are to predict how quickly the tumour might grow or spread.

Assessing grade, in addition to staging, allows doctors to design the optimal lung cancer treatment strategy and predict how the cancer might respond to particular therapy options.

How staging influences treatment

The stages and grades directly guide the treatment for lung cancer by showing how advanced the disease is, whether it’s confined to a single lung lobe, has spread to distant organs, lymph nodes, or is limited to early stage or early stages.

Early-stage lung cancer (stages 1–2)

• Surgical removal of the tumour or a single tumour is a primary option, sometimes combined with chemotherapy.
• Stage IIa and other stage II diseases might need further treatments if the cancer has spread to nearby areas.

Locally advanced lung xancer (stage 3)

• A multi-step approach using radiation therapy, chemotherapy, or surgery, occasionally combined with targeted therapies.
• This stage often includes involvement of nearby lymph nodes, deeper lung tissues, or the chest wall.

Advanced-stage lung cancer (Stage 4)

• For stage IV or extensive stage, systemic treatments such as immunotherapy, chemotherapy, targeted therapy, and palliative care come into play.
• The goal is to manage symptoms, improve survival rates, relieve pain or chest pain, and maintain the best quality of life, even as the cancer spreads to other organs.