Aetiology and Pathology of Lung Cancer

Cigarette smoking is responsible for at least 85% of lung cancer cases in the UK. The risk is directly proportional to the amount and tar content of cigarettes smoked.

Passive smoking is a significant risk factor, contributing to 5% of all lung cancer deaths.

Adenocarcinoma is the most common type of lung cancer, representing approximately 35-40% of cases.

Squamous cell carcinoma, accounting for 25-30% of cases, develops from the squamous cells lining the bronchi.

Small cell lung cancer, constituting about 15% of cases, is known for its aggressive nature and tendency to spread rapidly.

Large cell lung cancer, representing 10-15% of cases, is a broadly defined category that includes various poorly differentiated cell types.

Lung cancer can spread locally to the pleura, chest wall, intercostal nerves, and brachial plexus.

Lung cancer often spreads through lymphatic vessels to mediastinal and supraclavicular lymph nodes.

Blood-borne metastases from lung cancer commonly occur in the liver, bone, brain, adrenal glands, and skin.

Lung cancer can manifest in various ways, including local symptoms, metastatic effects, and paraneoplastic syndromes.

A change in the character of a smoker's cough, especially if associated with other symptoms, should always raise suspicion of lung cancer.

Common in smokers, especially with central bronchial tumors. It may be caused by bronchitic infection, but always needs investigation to rule out lung cancer. Sometimes, central tumors invade large vessels, causing sudden, massive haemoptysis - a terminal event.

This can be the presenting symptom of lung cancer depending on the tumor's location. Complete obstruction causes collapse of a lobe or lung, leading to breathlessness, mediastinal displacement, and dullness to percussion with reduced breath sounds. Partial obstruction may cause a specific kind of wheeze and can impair drainage of secretions, potentially causing pneumonia or lung abscess.

A harsh inspiratory noise (wheezing) that occurs when the larynx, trachea, or main bronchus is narrowed by the primary tumor or by compression from lymph node enlargement.

Can be caused by collapse of a lobe or lung, pneumonia, a large pleural effusion, or compression of the phrenic nerve leading to diaphragmatic paralysis.

Pleural pain may indicate malignant pleural invasion, although it can occur with distal infection. Intercostal nerve involvement causes pain in a specific area of the chest wall. Cancer in the lung apex may cause Horner syndrome (ipsilateral partial ptosis, miosis, and hypohidrosis of the face) due to involvement of the sympathetic nerves to the eye. Pancoast syndrome (pain in the inner aspect of the arm, sometimes with small muscle wasting in the hand) indicates malignant destruction of the T1 and C8 roots in the lower part of the brachial plexus by an apical lung tumor.

Involvement of the esophagus may cause dysphagia. If the pericardium is invaded, arrhythmia or pericardial effusion may occur. Obstruction of the superior vena cava by malignant nodes causes swelling of the neck and face, conjunctival edema, headache, and dilated veins on the chest wall - most commonly due to lung cancer. Involvement of the left recurrent laryngeal nerve by tumors at the left hilum causes vocal cord paralysis, voice alteration, and a 'bovine' cough. Supraclavicular lymph nodes may be palpably enlarged or identified using ultrasound; if so, a needle aspirate may provide a simple means of cytological diagnosis.

This can lead to focal neurological defects, epileptic seizures, personality change, jaundice, bone pain, or skin nodules. Lassitude, anorexia, and weight loss usually indicate metastatic spread.

Overgrowth of the soft tissue of the terminal phalanx, leading to increased nail curvature and nail bed fluctuation, is often seen.

This is a painful periostitis of the distal tibia, fibula, radius, and ulna, with local tenderness and sometimes pitting edema over the anterior shin. X-rays reveal subperiosteal new bone formation. While most frequently associated with lung cancer, HPOA can occur with other tumors.