Lung cancer is the main cause of death due to cancer in the US accounting for more deaths than prostate, breast and colon cancers combined. Statistics in the UK are also similar and interestingly more women die due to lung cancer than breast cancer

CAUSES AND RISK FACTORS OF LUNG CANCER
Nearly 90 percent of lung cancer cases is caused by smoking, both active and passive. Cigarette smoke contains several harmful chemicals or carcinogens and when inhaled lung tissue is damaged. With repeated exposure to cigarette smoke, the capacity of the lungs to repair the damage decreases and the damaged lung cells begin to show abnormal changes and cancer develops

Risk Factors
• Smoking (both active and inhalation of second hand smoke)
• Increasing age
• Family history of lung cancer
• Previous history of radiation therapy to chest
• Chronic obstructive pulmonary disease
• Radon gas exposure – due to degrading of uranium in the soil
• Occupational exposures – asbestos, arsenic, chromium, nickel, cadmium
• Increased expression of epidermal growth factor receptor (EGFR) and its ligands in non-small cell lung cancer (NSCLC)

TYPES OF LUNG CANCER
The two broad types of lung cancer include non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). They behave clinically differently

• Non-small Cell Lung Cancer
Account for about 85% of cases
Includes squamous cell cancer, adenocarcinoma, large cell adenocarcinoma, carcinoid tumors and bronchoalveolar cancer
Exhibit similar clinical behavior

• Small Cell Lung Cancer
Accounts for approximately 15% lung cancers
Occurs almost exclusively in smokers
Grows rapidly and spreads faster; mostly advanced and inoperable at presentation
Responsive to chemotherapy but prognosis remains poor

CLINICAL FEATURES OF LUNG CANCER
In the early stages, lung cancer typically does not demonstrate any signs or symptoms. They usually become evident only when the disease is advanced. Clinical features include

• New onset cough that persists and does not respond to antibiotics
• Coughing up blood (hemoptysis)
• Shortness of breath (dyspnea)
• Chest pain
• Weakness and tiredness
• Fever
• Clubbing of fingers
• Hoarseness of voice
• Difficulty in swallowing
• Unintentional weight loss
• Bone pain
• Headache

COMPLICATIONS OF LUNG CANCER
• Severe bout of hemoptysis leading to shock
• Marked shortness of breath at rest
• Pleural effusion
• Pain due to infiltration of nerve
• Collapse of lung
• Metastatic disease – bony pain, liver enlargement, neurological signs and symptoms due to brain involvement, proximal myopathy, peripheral neuropathy

DIAGNOSIS OF LUNG CANCER
If a patient presents to the doctor with symptoms such as persistent cough and other chest symptoms, and the doctor has reasons to suspect a lung malignancy, the following tests may be performed

Imaging tests – An chest x-ray (CXR) may show an abnormal mass or nodule. A CT scan can detect smaller growths that might not be evident on an X-ray.

If initial tests point to a malignancy, further imaging tests such as CT-contrast or PET-CT scan should be performed to precisely localize the tumor, look for evidence of distant metastases and stage the cancer before treatment

Sputum/pleural fluid cytology – If there is cough and sputum production, examining the sputum under the microscope may show presence of lung cancer cells. May be advisable in patients with central lung lesions and those unwilling to undergo or unable to tolerate more invasive tests

Neck ultrasound – If CT scan is suspicious for lung malignancy, ultrasound imaging of neck is advised with sampling of visible lymph nodes or non-ultrasound-guided transbronchial needle aspiration (TBNA).

Endobronchial ultrasound (EBUS) – If neck ultrasound is negative, endobronchial ultrasound and fine needle aspiration should be done

Bronchoscopy and biopsy – During a bronchoscopy, a thin illuminated tube into the airways to obtain a sample of the tumor and assess tumor operability

Other methods to obtain biopsy – If less invasive methods fail to yield tissue sample, percutaneous transthoracic needle biopsy, anterior mediastinoscopy, surgical biopsy of tumor and biopsy of metastases if these are more accessible

Molecular testing – Presence of EGFR mutation may help decide mode of treatment in NSCLC

STAGING OF LUNG CANCER
Staging system of any cancer is done by clinicians to determine extent and spread of disease and decide the best line of management

Stages of NSCLC
• Stage 1: Cancer limited to lung
• Stage 2: Cancer within lung and spread to nearby lymph nodes
• Stage 3: Cancer within lung and involvement of lymph nodes in the middle of the chest.
• Stage 3A: Cancer is found in lymph nodes, but only on the same side of the chest where cancer is present
• Stage 3B: Cancer involving lymph nodes on the opposite side of the chest and/or lymph nodes above the collarbone.
• Stage 4: Cancer involving both lungs and adjacent tissue, or spread to distant organs.

Stages of SCLC
SCLC has two main stages
• Limited stage – Cancer limited to one lung and adjacent lymph nodes on the same side of the chest.
• Extensive stage
Opposite lung involvement
Lymph nodes on the opposite side
Pleural effusion +
Bone marrow involvement
Distant organ spread

TREATMENT OF LUNG CANCER
Treatment of lung cancer will vary from one person to another and depends on stage of disease and health status of the patient

• NSCLC
Stage 1 – Surgery to remove a small part of the lung. Chemotherapy may also be advised, especially if there is risk of recurrence
Stage 2 – Surgery to remove a portion of or entire lung. Chemotherapy is also generally advised.
Stage 3 – Combination of chemotherapy, surgery, and radiotherapy.
Stage 4 – Harder to cure. Treatment options include surgery, palliative care, chemotherapy, radiation, targeted therapy, and immunotherapy.

• SCLC
Options for small cell-lung cancer (SCLC) also include surgery, chemotherapy, and radiotherapy although the cancer may be too advanced for surgery. Patients may benefit from palliative care that aims to reduce pain and other symptoms and keep the patient comfortable

PREVENTION OF LUNG CANCER
Although it may not always be possible to prevent lung cancer, the risk can be reduced by

• Quit smoking and avoid second hand smoke
• Avoid occupational exposures
• Test your home and surroundings for radon
• Eat a healthy diet rich in fresh fruits, vegetables and fiber
• Exercise regularly and maintain a healthy weight