Almost all types of lung cancer are carcinomas. The term carcinoma means that the tumour cells derive from an epithelial cell, which is the kind of cell existing on the surface of the airways.

Lung carcinomas are divided into two main groups based on how the cancer cells look: small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC). To know the kind of lung cancer is very important, because SCLC and NSCLC have different clinical characteristics and treatment. The NSCLC is the most common, representing 85% of all lung cancers.4

Staging

The stage of cancer identifies the extent of cancer in the body. This is used to plan the treatment.

In general, doctors try to diagnose and stage the cancer at the same time. This involves several tests.

In the staging system called AJCC (American Joint Committee on Cancer), the letters T, N and M identify different areas of cancer growth. The T score indicates how large and where the primary tumour is. The N score indicates how far lung cancer has spread within nearby lymph nodes. And the M score indicates that the cancer has spread to parts of the body other than the lung in which it started. The combination of TNM scores assigns the stage of the cancer. In lung cancer, this stage ranges from 0 to IV3:

• Occult carcinoma: The primary tumour has not been found. Lung cancer cells have been detected in fluids or mucus from the lungs, and there are no signs of lung cancer in other parts of the body.
• Stage 0: There are cancer cells in airways, but they have not grown into lung tissue or spread outside the lung.
• Stages I, II, III: Cancer cells have grown into the lung tissue. Some have spread to nearby lymph nodes, but they have not spread to parts of the body far from the primary tumour in the chest.
• Stage IV: This is the metastatic stage, which means that lung cancer cells have spread to parts of the body far from the primary tumour in the chest.  

Prevalence and prognosis

Lung cancer is the most common cancer diagnosed (excluding keratinocyte carcinoma, a skin cancer) and the greatest cause of cancer-related death. Lung cancer represents 17% of all cancers in men and 9% of all cancers in women.5

The incidence and mortality rates of lung cancer are higher in countries with higher socioeconomic development, and some countries have a declining trend in men but an increasing trend in women.6

Several factors, such as age, sex, lung function, body constitution, concurrence of other diseases, histopathological type, spread of the tumour, and treatment influence the prognosis in lung cancer. Prognosis of the non-small-cell lung cancer is better than that of the small-cell lung cancer.

Considering the degree of spread of the lung cancer, the disease can be:

• Localised: When there is no sign indicating the cancer has spread beyond the lung. It has a better prognosis than cancer that has spread further (regional or distant lung cancer).
• Regional: When the cancer has spread outside the lung but only to nearby lymph nodes. It has a better prognosis than distant lung cancer.
• Distant: When the cancer has spread to distant parts of the body, such as the brain, bones, liver or the other lung.

The best prognosis is always for localised lung cancer. In 2010, the prognosis at 5 years for localised lung cancer had an average survival rate of 58.2 %.

The survival rate at 5 years is different depending on the histologic subtype and the stage of cancer.