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Lung Cancer

Epidemiology of Cancers: Lung Cancer

Description
There are 2 main types of lung cancer:

  1. Small cell lung cancer (SCLC) - accounts for 10-30% of lung cancers. The most aggressive form of the disease and is often inoperable.
     
  2. Non small cell lung cancer (NSLC) - The most common type of lung cancer accounting for around 80% of cases.

There are 3 types of NSLC:

Squamous cell carcinoma
Accounts for 30-50% of lung cancers - strongly associated with smoking.

Adenocarcinoma
Accounts for 10-30% of lung cancers. The incidence of adenocarcinoma is increasing1.

Large cell carcinoma
Accounts for 5-15% of lung cancers1.

Symptoms

  • Up to 25% of cases are asymptomatic
  • Cough, sometimes with haemoptysis.
  • Recurring pneumonia and bronchitis.
  • Chest pain.
  • Hoarseness.
  • Locally advanced and metastatic disease may cause a range of symptoms including; breathlessness, obstruction of the airway and oesophagus, enlarged lymph nodes, anorexia, weight loss1.

Epidemiology

  • Lung cancer is the most common malignant neoplasm in most countries1. An estimated 1.3 million cases occur worldwide each year.
  • The geographic distribution of lung cancer incidence directly reflects patterns in tobacco consumption. An increase in tobacco consumption is paralleled some 20 years later by an increase in the incidence of lung cancer, while a decrease in consumption is followed by a decrease in incidence1.
  • Worldwide the highest rates of lung cancer are in Europe (especially eastern Europe) and North America.
  • Lung cancer is the second most common cancer in the UK (after breast cancer), with around 38,000 new cases diagnosed each year2.
  • The incidence is higher among men than women, though the incidence in women is increasing.
  • The incidence of lung cancer is low in persons under age 40 and increases markedly; peaking in persons aged 75-84 years2.
  • Lung cancer is the most common cause of death from cancer in the UK, accounting for 24% of all male cancer deaths and 18% of all female cancer deaths. In 2004 there were 33,044 deaths from lung cancer in the UK, 19,493 among males and 13,551 among women (giving a male to female ratio of 3:2)2.
  • Over 75% of all deaths from lung cancer occur in persons aged >65 years.
  • Lung cancer mortality rates among males has declined in age-groups since the early 1980s. For women rates declined in the 55-64 age since the late 1980s and in the 65-74 age group wince the mid 1990s. and in the 65-74 age group since the mid 1990s. declining for all age groups in the UK since the early 1980s2.
  • Lung cancer incidence and mortality rates are strongly associated with deprivation. In developed countries the risk of lung cancer among men is 2-3 fold higher in lower than higher socio-economic groups 1,2.
  • Lung cancer has a poor prognosis and one of the lowest survival outcome for any cancer. In England and Wales around 25% of patients are alive one year after diagnosis and 7% at five years2.

Risk Factors

Smoking
Smoking is the single most important cause of lung cancer responsible for 80-90% of lung cancers. The risk among smokers is between 10 and 20 times greater than for non-smokers.

Smoking has been linked with all four histological types of lung cancer, but less so with adenocarcinoma, which is the commonest type among non-smokers.

The risk of lung cancer is related to a number of factors including, the number of cigarettes smoked, duration of smoking, pattern of smoking, tar content, time since quitting, age started smoking and inhalation pattern.

Passive Smoking
Environmental tobacco smoke is also a risk factor.

Environmental carcinogens
Exposure to carcinogens including asbestos, radon, arsenic, polycyclic hydrocarbons, nickel and chromium.

Asbestos - the risk in those exposed to asbestos is around 5-7 times the risk on those unexposed. Smokers who work in the asbestos industry are at 93 times higher risk than non-smokers not exposed to asbestos.

Radon - increased lung cancer risk was first observed in uranium miners with high radon exposure levels. Residential radon exposure may account for 5% of lung cancers in England and Wales2.

Previous infection with pulmonary tuberculosis and pneumonia

Diet
There is some evidence that a diet rich in fruits and vegetables may provide a protective effect against lung cancer1.  Beta-carotene supplementation may increase lung cancer mortality in smokers2.

Screening and Prevention
There is currently no effective screening procedures for lung cancer.
Reductions of tobacco consumption remain the primary preventative measures for reducing the global burden of lung cancer.

Genetic susceptibility
Some family studies indicate that an inherited gene or genes, combined with smoking, increases the risk of lung cancer. 

References

  1. Adami, HO, Hunter D, Trichopoulos D, eds. Textbook of Cancer Epidemiology, Oxford University Press: New York, 2002.
     
  2. Cancer Research UK http://info.cancerresearchuk.org:8000/cancerstats/

Further Resources

The International Lung Cancer Consortium http://ilcco.iarc.fr/index.php

© CM Kirwan 2006