What Is Lung Cancer

In Singapore, lung cancer has the highest mortality rate among males and the third highest among females. According to the Singapore Cancer Registry 2019 Annual Report, lung cancer made up 25.6% of cancer deaths in males and 15.5% of deaths in females in Singapore between 2015-2019.

Lung cancer starts when abnormal cells grow and multiply in an uncontrolled way. Lung cancer begins in the lungs and may spread to lymph nodes or other organs in the body.  If cancer begins in another part of the body and spreads to the lungs it is known as secondary or metastatic cancer in the lung.

Categories Of Lung Cancer

Lung cancers are usually grouped into two main types: small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). This is diagnosed based on how the cells look under a microscope.

Non-Small Cell Lung Cancer (NSCLC)

NSCLC is the more common type of lung cancer, comprising approximately 85% of lung cancers. It is less aggressive and spread less quickly than SCLC. If discovered early, surgery and/or radiation therapy, or chemotherapy may be used as treatment.

There are sub-types of non-small cell lung cancer. The most common are: 

• adenocarcinoma – begins in mucus-producing cells and makes up about 40% of lung cancers. While this type of lung cancer is most commonly diagnosed in current or former smokers, it is also the most common lung cancer in non-smokers. 
• squamous cell (epidermoid) carcinoma - commonly develops in the larger airways of the lung. 
• large cell undifferentiated carcinoma - can appear in any part of the lung and is not clearly squamous cell or adenocarcinoma. 

Small Cell Lung Cancer (SCLC)

SCLC is fast-growing, aggressive, and rapidly spreads through the bloodstream and lymphatics to other parts of the body. Though not as common, it is often advanced at diagnosis. It is usually treated with chemotherapy alone or in combination with radiotherapy.

Other Types Of Lung Tumours

Along with the main types of lung cancer, other tumours can occur in the lungs.

• Lung carcinoid tumours: Carcinoid tumours of the lung account for fewer than 5% of lung tumours. Most of these grow slowly.
• Other lung tumours: Other types of lung cancer such as adenoid cystic carcinomas, lymphomas, and sarcomas, as well as benign lung tumours such as hamartomas are rare. These are treated differently from the more common lung cancers and are not discussed here.
• Cancers that spread to the lungs: Cancers that start in other organs (such as the breast, pancreas, kidney, or skin) can sometimes spread (metastasize) to the lungs, but these are not lung cancers. For example, cancer that starts in the breast and spreads to the lungs is still breast cancer, not lung cancer. Treatment for metastatic cancer to the lungs is based on where it started (the primary cancer site).