Lung Cancer Overview

Prevalence and Impact

Lung cancer ranks as the third most common cancer in North America and is the leading cause of cancer-related deaths. Approximately 14% of all new cancer diagnoses are lung cancers, which account for 25% of all cancer fatalities.

Understanding Tumours

Lung cancer originates in the lung cells, forming a malignant tumour that can invade surrounding tissues. A tumour consists of a cluster of cells that proliferate abnormally. Non-cancerous tumours, such as hamartoma or papilloma, differ from cancerous tumours, which can grow uncontrollably and metastasize, spreading cancer cells to other body parts. Lung metastasis refers to cancer that has spread to the lungs from another site in the body, requiring different treatment approaches compared to primary lung cancers.

Primary Lung Cancer vs. Pleural Mesothelioma

Primary lung cancer, also known as bronchogenic carcinoma, begins in the lungs, while pleural mesothelioma arises from the pleura covering the lungs. The treatment and prognosis for pleural mesothelioma differ significantly from those for primary lung cancer.

Types of Lung Cancer

Non-Small Cell Lung Cancer (NSCLC)

Non-small cell lung cancers constitute 80-85% of lung cancer cases. This type typically begins in the glandular tissue of the lung, specifically in cells responsible for mucus production. Several subtypes of NSCLC include:

– **Adenocarcinomas**: The most prevalent form, arising in glandular tissues. It can affect both smokers and non-smokers and is particularly common among women and younger individuals.

– **Squamous Cell Carcinoma**: Common in smokers, this type originates in the squamous cells lining the bronchi.

– **Large Cell Carcinoma**: A less common form of NSCLC.

– **Sarcoma and Sarcomatoid Carcinoma**: Both are rare variants.

Small Cell Lung Cancer (SCLC)

Small cell lung cancers typically develop in the cells lining the bronchi and include small cell carcinoma and combined small cell carcinoma.

Risk Factors

Key Risk Factors

While lung cancer can affect anyone, smoking remains the primary risk factor. Individuals with a history of over 30 pack years of smoking are at the highest risk.

– **Age**: The risk of lung cancer increases with age, with over half of new cases occurring in those over 60. The average age of diagnosis is 70.

– **Sex**: Lung cancer is more prevalent in men, correlating with higher smoking rates among males.

– **Ethnicity**: Research indicates that black men are 20% more likely to develop lung cancer compared to white men, while black women are 10% less likely than their white counterparts.

Modifiable Risk Factors

Approximately 45% of lung cancer cases are linked to modifiable risk factors, including:

– Tobacco smoking
– Second-hand smoke exposure
– Radon and asbestos exposure
– Occupational chemical exposure
– Outdoor air pollution
– Family history of lung cancer
– Personal history of lung disease
– Exposure to radiation and arsenic in drinking water

Screening for Lung Cancer

Screening Methods

Early detection of lung cancer is vital for successful treatment. However, conventional methods like chest X-rays and sputum tests are not recommended due to their ineffectiveness.

– **Low-Dose CT Scans**: Studies have shown that low-dose computed tomography (LDCT) can detect cancer in asymptomatic individuals. The National Lung Screening Trial demonstrated that participants receiving LDCT had a 20% lower mortality rate from lung cancer compared to those screened with X-rays.

The Canadian Task Force on Preventive Health Care recommends annual LDCT screening for high-risk individuals, defined as those aged 50-74 who are current or recent smokers with a significant smoking history.

Potential Risks of Screening

While screening can lead to early diagnosis, it also carries risks such as radiation exposure, false positives, and complications from follow-up tests.

Symptoms of Lung Cancer

Early-stage lung cancer may present no symptoms, and many patients experience signs only in later stages. Common symptoms include:

– Persistent cough or worsening cough
– Shortness of breath
– Wheezing
– Chest pain, particularly during deep breaths or coughing
– Blood in sputum
– Recurring chest infections
– Unexplained weight loss and fatigue
– Hoarseness or voice changes
– Difficulty swallowing
– Swollen lymph nodes
– Fluid buildup around the lungs

Paraneoplastic syndromes, which are effects of substances produced by cancer cells, can also present various symptoms, such as hypercalcemia associated with squamous cell carcinoma.

Diagnosis of Lung Cancer

Diagnosis involves a combination of health history, physical examinations, imaging, and lab tests. Key diagnostic tests include:

– **Chest X-rays**: Initial tests to identify abnormalities.
– **CT Scans**: Provide detailed images of the lungs.
– **PET Scans**: Assess cancer spread.
– **MRI**: Offers cross-sectional images of organs.
– **Ultrasound**: Used for fluid assessment and biopsy guidance.
– **Biopsy**: Confirmatory test for cancer, involving tissue sampling.

Staging Lung Cancer

Staging determines the tumor size and extent of spread, crucial for treatment planning. NSCLC is staged from 0 to IV, while SCLC is classified as limited or extensive.

Stage 0 indicates cancer confined to the airway lining, while stage IV indicates metastasis to other lungs or body parts. Accurate staging informs treatment choices as effective therapies may vary by stage.

Treatment Options

Treatment approaches depend on cancer type, stage, and advancement, including:

– **Surgery**: Considered for early-stage NSCLC, options include pneumonectomy, lobectomy, segmentectomy, and video-assisted thoracic surgery (VATS).

– **Radiation Therapy**: Targets cancer cells using high-energy radiation, often combined with surgery or chemotherapy.

– **Chemotherapy**: Involves intravenous drugs to kill cancer cells, with various potential side effects.

– **Targeted Therapy**: Focuses on specific cancer cell characteristics.

– **Immunotherapy**: Utilizes the patient’s immune system to combat cancer cells, effective in certain NSCLC cases.

Conclusion

Lung cancer remains the leading cause of cancer mortality, yet it is largely preventable. Avoiding tobacco smoke and participating in recommended screenings can significantly reduce the risk and enhance early detection. Support resources are available for individuals diagnosed with lung cancer, including networks and information from organizations like the Canadian Cancer Society and local cancer clinics.

Written by Lisa Borsellino, BSc

References

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