Lung cancer begins in lung tissue and may spread to lymph nodes and other parts of the body, such as the brain.
 
There are two main types of lung cancer:

The term “small cell” refers to the size and shape of cancer cells seen under a microscope. It is important for doctors to recognize the difference between these two types of cancer because each is treated differently.
 
Within non-small cell lung cancer, two large groups can be distinguished, those with squamous cell histology and those with non-squamous subtypes or adenocarcinomas. This differentiation is relevant when deciding on treatment (when advanced-stage chemotherapy is needed).
 
 

All imaging investigations (CT, MRI, PET-CT) obtain information necessary to determine which other organs, apart from the lung,are affected. Knowing how the cancer has spread is essential to establish the stage of the disease, since the stage is relevant for prognosis and treatment. Decisions are made on the treatment of patients with lung cancer depending on the stage (amongst other factors).

The stage is defined by three variables:
 

• T for tumour: establishes the size of the lung cancer and whether or not it is in contact with neighbouring structures. There are 4 levels:T1 (1a(mi), 1a, 1b, 1c) T2a/T2b, T3, T4, depending on its extension.

 

• N for nodes: describes whether or not there is involvement of lymph nodes around the tumour on radiological investigation. There are 4 categories:
  • N0(when there are no nodes)
  • N1 When the nodes are on the same side as the tumour and do not involve the mediastinum,
  • N2 when there are nodes in the mediastinum on the same side as the tumour.
  • N3 when there are contralateral mediastinal nodes, and/or supraclavicular nodes (above the clavicle) regardless of whether they are on the same side as the lung cancer or not.

 

• M for metastasis: identifies whether or not there is distant metastasis. There are 2 major categories:
  • M0when there is no metastasis
  • M1 when there is.
    • M1a: if there is metastasis in the contralateral lung or pleura
    • M1b:when there is a single metastasis in an organ other than the lung.
    • M1c: when metastases exist in different organs.

 
The combination of T, N, and M with the different numbers establishes the stage of the disease, which can be from stage I and II, considered to be localised disease, stage III or locally advanced disease, to stage IV or metastatic disease.