The term lung cancer, or bronchogenic carcinoma, refers to malignancies that originate in the airways or pulmonary parenchyma. Lung cancer is the most common cancer worldwide.¹ It is also the leading cause of cancer mortality in Ireland, representing approximately 20% of all deaths due to cancer.² 

In Ireland, lung cancer is the third most common cancer in both men and women, accounting for 13.9% of cancers in men and 9.4% in women during the years 1994-2008 (excluding non-melanoma skin cancer).³ Between 1994 and 2008, on average 1,059 men and 652 women a year were diagnosed with lung cancer in this country.³

International comparisons show that the incidence and mortality rates for Irish men compare quite favourably with our European neighbours.³ The incidence and mortality rates for women, however, are among the highest in Europe.³ Fewer than 1% of lung cancer cases occur before the age of 40. The rates rise steeply after age 40 and peak at 65-75 years.² Earlier diagnosis, efficient and correct diagnosis and staging, and modern multidisciplinary management have led to improved short and long-term survival with good quality of life. 

Despite advances in radiotherapy and chemotherapy, surgery remains the only effective curative treatment for lung cancer.² However, the prevailing attitude to lung cancer, even among healthcare professionals, is one of pessimism due to poor overall survival rates, even in the minority of patients who present with apparent early-stage disease. Irish five-year survival figures are approximately 8% for men and 10% for women.²

Causes of lung cancer

Smoking is the major cause of lung cancer. It is estimated that 90% of cases can be directly attributed to tobacco smoking.² The prevalence of smoking in Ireland remains over 20%, with peak prevalence over 30% in the 25-34-year-old age group.² Duration of smoking is the strongest determinant of risk among smokers; the earlier the starting age, or the longer the period of smoking, the higher the risk. For smokers, the risk for lung cancer is on average 10-fold higher than in lifetime non-smokers. Stopping smoking at any age, but particularly before middle-age, avoids most of the subsequent risk. 

Passive smoking is a cause of lung cancer in those who have never smoked. Because smoking is a modifiable risk factor, if progress is to be made in reducing the incidence of lung cancer in Ireland in the future, renewed efforts must be made to reduce tobacco use, especially in women.

Environmental factors have also been associated with an increased risk for developing lung cancer. These include exposure to asbestos, radon, metals (arsenic, chromium and nickel) and ionising radiation. Asbestos exposure and cigarette smoking may exert a synergistic effect on lung cancer risk. Various other lifestyle factors such as alcohol intake and physical activity may be related, but the evidence is inconsistent.

Types of lung cancer

Approximately 95% of all lung cancers are classified as either small cell lung cancer (SCLC) or non-small cell lung cancer (NSCLC). NSCLC is any type of epithelial lung cancer other than SCLC. The most common types of NSCLC are squamous cell carcinoma, large cell carcinoma and adenocarcinoma, but several other types also occur and all types can occur in unusual histologic variants. This distinction between NSCLC and SCLC is essential for staging, treatment and prognosis. 

Squamous cell lung cancer

Squamous cell lung cancer is more common in males and is closely correlated with a history of tobacco smoking. It most often arises centrally in larger bronchi. While it often metastasises to locoregional lymph nodes early in its course, it generally disseminates outside the thorax somewhat later than other major types of lung cancer. Large tumours may undergo central necrosis, resulting in cavitation. 

Adenocarcinoma of lung

Adenocarcinomas account for approximately 40% of lung cancer. It is the most common type of lung cancer in non-smokers. Adenocarcinomas are more often seen peripherally in the lungs.

Small cell lung cancer 

SCLC, or oat cell carcinomas, arise in peribronchial locations and infiltrate the bronchial submucosa. SCLC accounts for approximately 15% of bronchogenic carcinomas. 

Widespread metastases occur early in the course of the disease, with common spread to the mediastinal lymph nodes, liver, bones, adrenal glands and brain. In addition, production of various peptide hormones can lead to a wide range of paraneoplastic syndromes.

Signs and symptoms

Lung cancer may present with symptoms or may be found incidentally on imaging. Currently, over 75% of patients present with locally advanced stage or disseminated disease.² This may reflect the aggressive biology of the disease or the frequent absence of symptoms until locally advanced or metastatic disease is present. Approximately 75% of patients have one or more symptoms at the time of diagnosis.

Clinical manifestations of lung cancer are dependent on the location and size of the tumour. The intrathoracic effects of the tumour can result in cough, haemoptysis, shortness of breath or chest pain. Symptoms may also result from local invasion or compression of adjacent thoracic structures such as compression of the oesophagus causing dysphagia, compression of the laryngeal nerves causing hoarseness, or compression of the superior vena cava causing facial oedema and distension of the superficial veins of the head and neck.

Symptoms from distant metastases may also be present and can result in neurological deficits or personality change from brain metastases, or bone pain from metastatic bone disease. Patients may also complain of systemic symptoms of fatigue, malaise and weight loss. Infrequently, patients may present with symptoms and signs of paraneoplastic disease such as hypertrophic osteoarthropathy with digital clubbing or hypercalcaemia of malignancy from parathyroid hormone-related protein. Physical examination may reveal enlarged supraclavicular lymphadenopathy, pleural effusion or signs of associated diseases such as chronic obstructive pulmonary disease.

Initial evaluation

The main issues to assess in a patient with a suspected lung cancer are the cell type (NSCLC versus SCLC) and the stage of disease. A history and physical examination is part of the initial patient assessment. The functional status of the patient, which includes an assessment of the patient’s general health and medical comorbidities, must also be made (see Table 1). 

Routine laboratory evaluations should also be performed. A chest x-ray is the most common first diagnostic step. 

A computerised tomography (CT) scan should be performed of the thorax, abdomen and pelvis to examine for intra-thoracic disease and to establish the presence of metastatic disease (ie. in the liver or adrenal glands). 

A CT brain scan may be performed to evaluate the presence and extent of metastases in the brain. An isotope bone scan may help identify the presence of bone metastases. 

Magnetic resonance imaging (MRI) scans may be appropriate when precise detail about a tumour’s location is required. Positron emission tomography (PET) scans can also be useful if the patient is being considered for surgery. This may be integrated with CT scanning in a technique known as PET-CT. Integrated PET-CT has been shown to improve the accuracy of staging over PET scanning alone.

A tissue diagnosis is always necessary prior to treatment. If a tumour is centrally located a sputum cytology examination may allow histological diagnosis. A central tumour may also be accessible to sampling using bronchoscopy. Fine needle aspiration (FNA) is particularly useful when a tumour is peripherally located and not accessible to sampling by bronchoscopy. 

All patients should be discussed at a multidisciplinary forum with access to a full lung cancer team so that appropriate primary treatment and follow-up can be arranged efficiently and effectively.³

References 

1. WHO. Cancer. Factsheet No. 297. Oct 2011. Available at http://www.who.int/mediacentre/factsheets/fs297/en/
2. Lung Cancer sub committee. Guidelines for the diagnosis and treatment of Lung Cancer. 2009; Third edition. Available at http://www.irishthoracicsociety.com/images/uploads/file/ITSLungCancerGuidelinesFebruary2010.pdf
3. National Cancer Registry. Lung Cancer Incidence, Mortality, Treatment and Survival in the Republic of Ireland: 1994-2008. 2011. Available at http://www.ncri.ie/pubs/pubfiles/LungCancer2011.pdf