Lung cancer is a malignant tumour that starts in one or both of the lungs. Although sometimes abnormal growth in the cells can results in benign tumours, abnormal lung cell growth or development can also result in a malignant, or cancerous, tumour. The type of lung cancer will differs based on the type of cell in which the cancer develops. Lung cancers are thus divided into non-small cell lung cancers (NSCLC) and small cell lung cancers (SCLC) [1].
.jpg)
[2] The Lungs (Human Anatomy)
When you breathe, you use your lungs—a pair of spongy, air-filled organs located on either side of the chest—they are part of your respiratory system. The trachea (windpipe) brings in inhaled air into the lungs through branches, called bronchi. The bronchi divide into smaller and smaller branches (bronchioles) until they are microscopic in size. The bronchioles end in clusters of microscopic air sacs called alveoli, which help absorb oxygen into the blood and expel carbon dioxide from the blood [3]. The lungs are protected by a thin covering called the pleura [4].
Incidence and mortality
Lung cancer remains the leading cause of cancer death for both men and women in Canada and worldwide [5]. According to the 2014 World Cancer Report, approximately 1.59 million deaths worldwide were attributed to lung cancer in 2012 [7].
According the 2015 Canadian Cancer Statistics, it was estimated there would be20, 900 deaths in Canada in 2015, with an estimated 13,400 women being diagnosed with lung cancer with 10,000 dying of it, and an estimated 13,600 men being diagnosed with 10,900 dying of it [7][8]. In Canada, the incidence rate for lung cancer is higher in men than in women. For men, it has been on a steady decline since the mid-1980s, whereas the incidence rate in women only levelled off in 2006 [9].
[12] The age-standardized incidence rate (ASIR) is the number of new cases of cancer per 100,000 people, standardized to the age structure of the 1991 Canadian population to account for changes in age distribution over time.
Types of lung cancer
Non-small cells lung cancers (NSCLC) account for about 85-90 per cent of all lung cancers. There are three main subtypes of NSCLC: adenocarcinoma, squamous cell carcinoma and large cell carcinoma. While the subtypes are distinct in terms of size, shape, and chemical make-up, they are grouped together because the approach to treatment and prognosis (outlook) are usually quite similar. In addition, there are also several rare types of NSCLC tumours [13].
Adenocarcinoma: About 40 per cent of lung cancers are adenocarcinomas. Adenocarcinomas start in the early versions of the cells that would normally secrete substances such as mucus. This type of lung cancer is prevalent in current or former smokers, but is also the most common type of lung cancer seen in non-smokers. It is more common in women than in men, and more likely to occur in younger people than other types of lung cancer.
Adenocarcinoma is typically found in the outer parts of the lung. It tends to grow slower than other types of lung cancer, and is more likely to be found before it has spread outside of the lung.
People with a type of adenocarcinoma called adenocarcinoma in situ (previously called (bronchioloalveolar carcinoma) tend to have a better prognosis than those with other types of lung cancer.
Squamous cell (epidermoid) carcinoma: About 25 to 30 per cent of all lung cancers are squamous cell carcinomas. These cancers start in early versions of squamous cells, which are flat cells that line the inside of the airways in the lungs. They are often linked to a history of smoking and tend to be found in the middle of the lungs, near a bronchus.
Large cell (undifferentiated) carcinoma: This type of cancer accounts for about 10 to 15 per cent of lung cancers. It can appear in any part of the lung and tends to grow and spread quickly, which can make it harder to treat. A subtype of large cell carcinoma, known as large cell neuroendocrine carcinoma, is a fast-growing cancer that is very similar to small cell lung cancer.
Other subtypes: There are also a few other subtypes of non-small cell lung cancer, such as adenosquamous carcinoma and sarcomatoid carcinoma. These are much less common.
[14] Information taken from the American Cancer Society
Small cell lung cancer (SCLC), alternatively known as oat cell cancer, oat cell carcinoma and small cell undifferentiated carcinoma, constitutes about 10 to 15 per cent of all lung cancers [15]. This type of cancer occurs almost exclusively in smokers and is very rare in non-smokers. At least 80 per cent of all lung cancer deaths are caused by smoking and this number is likely even higher for SCLC [16].
SCLC is the most aggressive of the lung cancers. It usually starts in the bronchi in the centre of the chest growing very quickly and creating large tumours. They can metastasize to other parts of the body, including the brain, liver and bone [17]. As SCLC is a very fast growing cancer, the treatment methods for SCLC and NSCLC differ greatly.
Other types of lung tumours
Lung metastases
Primary lung cancer is a cancer that starts in the lungs themselves and lung metastases occur when a cancer spreads to the lungs from a different primary site. The lungs are one of the most common locations to where the cancers spread.
Large carcinoid tumours
Large carcinoid tumours are a type of lung cancer that make up around five per cent of all diagnosed lung cancers. Large carcinoid tumours are uncommon and usually grow slower than other types of lung cancers. They are composed of neuroendocrine cells. Neuroendocrine cells make hormones like adrenaline and similar substances. They are part of a system scattered throughout the body in organs like the lungs, stomach and intestines. In the lungs, this may help control air flow and blood flow and control the growth of other types of lung cells [18].
Lung neuroendocrine cells sometimes develop abnormally and can form tumors. Large cell neuroendocrine carcinoma (LCNEC) is a rare cancer. It is a subtype of non-small cell lung cancer (NSCLC). Although it shares some features with small cell lung cancers (SCLC) it is typically treated as a type of NSCLC [19].
Benign lung tumours
Benign lung tumours are non-cancerous growths that do not spread to other parts of the body. They are rare and not usually life threatening. Hamartomas, papillomas and adenomas are all benign lung tumours. Papillomas tend to grow in the bronchi and can cause symptoms when they block the flow of air. This can include coughing, wheezing, shortness of breath or coughing up blood [20].
References
[1] “What Is Lung Cancer?” Canadian Cancer Society. Canadian Cancer Society. Web. 12 Jan. 2016.
[2] The Lungs (Human Anatomy). Digital image. WebMD. WebMD, 2014. Web. 12 Jan. 2016.
[3] “The Lungs (Human Anatomy).” Lung Disease & Respiratory Health Center. WebMD, 2016. Web. 12 Jan. 2016.
[4] “What Is Lung Cancer?” Canadian Cancer Society. Canadian Cancer Society. Web. 12 Jan. 2016.
[5] “Lung Cancer.” Lung Cancer Canada. Lung Cancer Canada, 2016. Web. 12 Jan. 2016.
[6] “Cancer.” World Health Organization. World Health Organization, Feb. 2015. Web. 12 Jan. 2016.
[7] Canadian Cancer Society’s Advisory Committee on Cancer Statistics. Canadian Cancer Statistics 2015. Toronto, ON: Canadian Cancer Society; 2015.
[8] ibid.
[9] ibid.
[10] Canadian Cancer Society’s Advisory Committee on Cancer Statistics. FIGURE 1.5 Age-standardized Incidence Rates (ASIR) for Selected* Cancers, Females, Canada, 1986–2015. Digital image. Canadian Cancer Statistics 2015. Canadian Cancer Society, June 2015. Web. 12 Jan. 2016.
[11] Canadian Cancer Society’s Advisory Committee on Cancer Statistics. FIGURE 1.4 Age-standardized Incidence Rates (ASIR) for Selected* Cancers, Males, Canada, 1986–2015. Digital image. Canadian Cancer Statistics 2015. Canadian Cancer Society, June 2015. Web. 12 Jan. 2016.
[12] Canadian Cancer Society’s Advisory Committee on Cancer Statistics. Canadian Cancer Statistics 2015. Toronto, ON: Canadian Cancer Society; 2015
[13] “Malignant Tumours of the Lung.” Canadian Cancer Society. Canadian Cancer Society, n.d. Web. 12 Jan. 2016.
[14] “What Is Non-small Cell Lung Cancer?” Lung Cancer (Non-Small Cell). American Cancer Society, 3 Apr. 2015. Web. 13 Jan. 2016.
[15] What Is Small Cell Lung Cancer?” Lung Cancer (Small Cell). American Cancer Society, 9 Mar. 2015. Web. 13 Jan. 2016.
[16] “What Are the Risk Factors for Small Cell Lung Cancer?” American Cancer Society. American Cancer Society, 9 Mar. 2015. Web. 13 Jan. 2016.
[17] Gersten, Todd. “Lung Cancer – Small Cell.” MedlinePlus Medical Encyclopedia. U.S. National Library of Medicine, 9 Sept. 2013. Web. 13 Jan. 2016.
[18]”What Are Lung Carcinoid Tumors?” What Are Lung Carcinoid Tumors? American Cancer Society, 10 Apr. 2015. Web. 26 Jan. 2016.
[19] ibid.
[20] “Benign Tumours of the Lung.” Canadian Cancer Society. Canadian Cancer Society, 2011. Web. 26 Jan. 2016.