What is lung cancer?

Lung cancer starts in the cells of the lung. A cancerous (malignant) tumour is a group of cancer cells that can grow into and destroy nearby tissue. It can also spread (metastasize) to other parts of the body. When cancer starts in lung cells, it is called primary lung cancer.

The lung is part of the respiratory system. You use your lungs when you breathe. The lungs are in the chest, one on each side of the heart. The right lung has 3 main parts, called lobes. The left lung is a bit smaller and has 2 lobes. The lungs are cushioned and protected by a thin covering called the pleura.

Diagram of the location of the lungs
Diagram of the location of the lungs

Cells in the lung sometimes change and no longer grow or behave normally. These changes may lead to non-cancerous (benign) tumours such as hamartoma and papilloma. But in some cases, changes to lung cells can cause cancer.

Lung cancers are divided into non–small cell lung cancer and small cell lung cancer based on the type of cell in which the cancer started.

Non–small cell lung cancer usually starts in glandular cells on the outer part of the lung. This type of cancer is called adenocarcinoma. Non–small cell lung cancer can also start in flat, thin cells called squamous cells. These cells line the bronchi, which are the large airways that branch off from the windpipe (trachea) into the lungs. This type of cancer is called squamous cell carcinoma of the lung. Large cell carcinoma is another type of non–small cell lung cancer, but it is less common. There are also several rare types of non–small cell lung cancer. These include sarcoma and sarcomatoid carcinoma.

Small cell lung cancer usually starts in cells that line the bronchi in the centre of the lungs. The main types of small cell lung cancer are small cell carcinoma and combined small cell carcinoma (mixed tumour with squamous or glandular cells).

Other types of cancer can spread to the lung, but this is not the same disease as primary lung cancer. Cancer that starts in another part of the body and spreads to the lung is called lung metastasis. It is not treated in the same way as primary lung cancer. Find out more about lung metastasis.

A rare type of cancer called pleural mesothelioma is often mistakenly called a lung cancer. But pleural mesothelioma starts in the pleura covering the lung and is very different from cancer that starts in the lung.

Expert review and references

  • Stephen Lam, MD, FRCPC
  • Chiang A, Detterbeck FC, Stewart T, Decker RH, Tanoue L. Non–small cell lung cancer. DeVita VT Jr, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg's Cancer: Principles & Practice of Oncology. 11th ed. Philadelphia, PA: Wolters Kluwer; 2019: 48:618–670.
  • Hann CL, Wu MA, Rekhtman N, Rudin CM. Small cell and neuroendocrine tumors of the lung. DeVita VT Jr, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg's Cancer: Principles & Practice of Oncology. 11th ed. Philadelphia, PA: Wolters Kluwer; 2019: 49:671–699.
  • PDQ® Adult Treatment Editorial Board . Non–Small Cell Lung Cancer Treatment (PDQ®) – Patient Version . Bethesda, MD : National Cancer Institute ; 2020: https://www.cancer.gov/types/lung/patient/non-small-cell-lung-treatment-pdq.
  • PDQ® Adult Treatment Editorial Board . Small Cell Lung Cancer Treatment (PDQ®) – Patient Version. Bethesda, MD : National Cancer Institute ; 2020: https://www.cancer.gov/types/lung/patient/small-cell-lung-treatment-pdq.
  • American Cancer Society. What is Lung Cancer?. 2019.

The lungs

The lungs are located in the chest and are part of the respiratory system.

Cancerous tumours of the lung

Malignant tumours of the lung are cancerous growths that have the potential to spread (metastasize) to other parts of the body.

Non-cancerous lung tumours

A non-cancerous (benign) tumour of the lung is a growth that does not spread (metastasize) to other parts of the body. Non-cancerous tumours are usually not life-threatening.

Lung nodules

A lung nodule is a small area found in the lung, often during an imaging test such as an x-ray or CT scan.