Lung Cancer

Lung cancer is the third most common cancer in the UK behind breast and prostate cancer. Smoking is the biggest cause. Around 80% of lung cancers are thought to be preventable.

 

Basic Anatomy

Air enters the lung through the trachea, which splits into the left main bronchus and right main bronchus. These bronchi then split into lobar bronchi, segmental bronchi, bronchioles, then alveoli. Bronchi is pleural for bronchus.

The right lung has three lobes. The left lung has two lobes. The heart is on the left, leaving less room for an extra lobe. Both lungs have an oblique fissure separating the lobes. The right lung also has a horizontal fissure. Fluid may be seen in the fissures in acute heart failure and pulmonary oedema.

There is a membrane that surrounds the lungs called the pleura. There are two layers of this membrane, with a small amount of fluid between them (less than 20mls). These layers separate the lungs from the chest wall. Lubrication between the two layers allows the lungs to expand and move without creating friction with the chest wall.

Between the two layers, there is a potential space, called the pleural cavity. The two layers are usually touching each other, which is why it is only a potential space. There is negative pressure within the pleural cavity, pulling the two layers of the pleura together. As the chest wall expands, the negative pressure within the pleural cavity pulls the lungs outwards with the chest wall, causing them to expand.

A pleural effusion is when the potential space of the pleural cavity fills with excess fluid. This creates an inward pressure on the lungs, reducing the lung volume. A pneumothorax is when air gets into the pleural cavity.

 

Histology

The histological types of lung cancer can be broadly divided into:

  • Small cell lung cancer (SCLC) (around 20%)
  • Non-small cell lung cancer (around 80%)

 

Non-small cell lung cancer can be further divided into:

  • Adenocarcinoma (around 40% of total lung cancers) 
  • Squamous cell carcinoma (around 20% of total lung cancers)
  • Large-cell carcinoma (around 10% of total lung cancers)
  • Other types (around 10% of total lung cancers)

 

Small cell lung cancer cells contain neurosecretory granules that can release neuroendocrine hormones. This makes SCLC responsible for multiple paraneoplastic syndromes.

 

Mesothelioma

Mesothelioma is a lung malignancy affecting the mesothelial cells of the pleura. It is strongly linked to asbestos inhalation. There is a huge latent period between exposure to asbestos and the development of mesothelioma of up to 45 years. The prognosis is very poor. Chemotherapy can improve survival, but it is essentially palliative.

 

Presentation

  • Shortness of breath
  • Cough
  • Haemoptysis (coughing up blood)
  • Finger clubbing
  • Recurrent pneumonia
  • Weight loss
  • Lymphadenopathy – often supraclavicular nodes are the first to be found on examination

 

Extrapulmonary Manifestations

Lung cancer is associated with a lot of extrapulmonary manifestations and paraneoplastic syndromes. These are linked to different types and distributions of lung cancer. Exam questions commonly ask you to suggest the underlying cause of the paraneoplastic syndrome. Sometimes they can be the first evidence of lung cancer in an otherwise asymptomatic patient.

Recurrent laryngeal nerve palsy presents with a hoarse voice. It is caused by a tumour pressing on or affecting the recurrent laryngeal nerve as it passes through the mediastinum.

Phrenic nerve palsy, due to nerve compression, causes diaphragm weakness and presents with shortness of breath.

Superior vena cava obstruction is a complication of lung cancer. It is caused by direct compression of the tumour on the superior vena cava. It presents with facial swelling, difficulty breathing and distended veins in the neck and upper chest. “Pemberton’s sign” is where raising the hands over the head causes facial congestion and cyanosis. This is a medical emergency.

Horner’s syndrome is a triad of partial ptosis, anhidrosis and miosis. It can be caused by a Pancoast tumour (tumour in the pulmonary apex) pressing on the sympathetic ganglion.

Syndrome of inappropriate ADH (SIADH) can be caused by ectopic ADH secreted by a small cell lung cancer. It presents with hyponatraemia.

Cushing’s syndrome can be caused by ectopic ACTH secretion by a small cell lung cancer.

Hypercalcaemia can be caused by ectopic parathyroid hormone secreted by a squamous cell carcinoma.

Limbic encephalitis is a paraneoplastic syndrome where small cell lung cancer causes the immune system to make antibodies to tissues in the brain, specifically the limbic system, causing inflammation in these areas. This causes symptoms such as short term memory impairment, hallucinations, confusion and seizures. It is associated with anti-Hu antibodies.

Lambert-Eaton myasthenic syndrome can be caused by antibodies produced by the immune system against small cell lung cancer cells. These antibodies also target and damage voltage-gated calcium channels sited on the presynaptic terminals in motor neurones. This leads to weakness, particularly in the proximal muscles but can also affect intraocular muscles causing diplopia (double vision), levator muscles in the eyelid causing ptosis and pharyngeal muscles causing slurred speech and dysphagia (difficulty swallowing). Patients may also experience dry mouth, blurred vision, impotence and dizziness due to autonomic dysfunction.

 

Referral Criteria

The NICE guidelines on suspected cancer (updated January 2021) recommend offering a chest x-ray, carried out within 2 weeks, to patients over 40 with:

  • Clubbing
  • Lymphadenopathy (supraclavicular or persistent abnormal cervical nodes) 
  • Recurrent or persistent chest infections
  • Raised platelet count (thrombocytosis)
  • Chest signs of lung cancer

 

TOM TIP: Remember two key examination findings that would automatically indicate an urgent chest x-ray: finger clubbing and supraclavicular lymphadenopathy. These are quick things to check for and spotting them could lead to an early diagnosis, potentially saving a patient’s life.

 

They also recommend considering a chest x-ray in patients over 40 years old who have:

  • Two or more unexplained symptoms in patients that have never smoked
  • One or more unexplained symptoms in patients that have ever smoked

 

The unexplained symptoms that the NICE guidelines list are:

  • Cough
  • Shortness of breath
  • Fatigue
  • Chest pain
  • Weight loss
  • Loss of appetite

 

TOM TIP: It is worth noting that this is quite a vague list. It is very common for patients to present with vague symptoms of fatigue or shortness of breath, and your first thought might not be of lung cancer. If a 60 year old ex-smoker presents feeling “tired all the time”, with no other symptoms, these guidelines suggest considering an urgent chest x-ray to exclude lung cancer. Doctors often do a general examination and get a set of blood tests in patients with this presentation, but don’t always consider getting a chest x-ray.

 

Investigations

Chest x-ray is the first-line investigation in suspected lung cancer. Findings suggesting cancer include: 

  • Hilar enlargement
  • Peripheral opacity – a visible lesion in the lung field
  • Pleural effusion – usually unilateral in cancer
  • Collapse

 

Staging CT scan of chest, abdomen and pelvis is used to assess the stage, lymph node involvement and presence of metastases. This should be contrast-enhanced, using an injected contrast to give more detailed information about different tissues.

PET-CT (positron emission tomography) scans involve injecting a radioactive tracer (usually attached to glucose molecules) and taking images using a combination of a CT scanner and a gamma-ray detector to visualise how metabolically active various tissues are. They are useful in identifying areas that cancer has spread to by showing areas of increased metabolic activity.

Bronchoscopy with endobronchial ultrasound (EBUS) involves endoscopy with ultrasound equipment on the end of the scope. This allows detailed assessment of the tumour and ultrasound-guided biopsy.

Histological diagnosis requires a biopsy to check the type of cells in the tumour. This can be either by bronchoscopy or percutaneous biopsy (through the skin).

 

Treatment options

All treatments are discussed at an MDT meeting involving various consultants and specialists, such as pathologists, surgeons, oncologists and radiologists. This is to make a joint decision about the most suitable options for the individual patient.

Surgery is offered first-line in non-small cell lung cancer to patients that have disease isolated to a single area. The intention is to remove the entire tumour and cure the cancer. See below for more detail on surgery.

Radiotherapy can also be curative in non-small cell lung cancer when diagnosed early enough.

Chemotherapy can be offered in addition to surgery or radiotherapy in certain patients to improve outcomes (“adjuvant chemotherapy”) or as palliative treatment to improve survival and quality of life in later stages of non-small cell lung cancer (“palliative chemotherapy“).

Treatment for small cell lung cancer is usually chemotherapy and radiotherapy. Prognosis is generally worse for small cell lung cancer compared with non-small cell lung cancer.

Endobronchial treatment with stents or debulking can be used as part of palliative treatment to relieve bronchial obstruction caused by lung cancer.

 

Lung Cancer Surgery

There are several options for removing a lung tumour:

  • Segmentectomy or wedge resection involves taking a segment or wedge of lung (a portion of one lobe)
  • Lobectomy involves removing the entire lung lobe containing the tumour (the most common method)
  • Pneumonectomy involves removing an entire lung

 

The types of surgery that can be used are:

  • Thoracotomy – open surgery with an incision and separation of the rib to access the thoracic cavity
  • Video-assisted thoracoscopic surgery (VATS) – minimally invasive “keyhole” surgery
  • Robotic surgery 

 

Minimally invasive surgery (i.e., VATS or robotic surgery) is generally preferred as it has a faster recovery and fewer complications.

 

There are three main thoracotomy incisions:

  • Anterolateral thoracotomy with an incision around the front and side
  • Axillary thoracotomy with an incision in the axilla (armpit)
  • Posterolateral thoracotomy with an incision around the back and side (the most common approach to the thorax)

 

TOM TIP: If you see a patient with a thoracotomy scar in your OSCEs, they are likely to have had a lobectomy, pneumonectomy or lung volume reduction surgery for COPD. If they have no breath sound on that side, this indicates a pneumonectomy rather than lobectomy. If they have absent breath sound in a specific area on the affected side (e.g., the upper zone), but breath sounds are present in other areas, this indicates a lobectomy. Lobectomies and pneumonectomies are usually used to treat lung cancer. In the past, they were often used to treat tuberculosis, so keep this in mind in older patients. If it is a cardiology examination and they have a right-sided mini-thoracotomy incision, this is more likely to indicate previous minimally invasive mitral valve surgery.

 

Chest Drains

A chest drain will be left in after thoracic surgery. The chest drain allows air and fluid to exit the thoracic cavity and the lungs to expand. A chest drain pump can be used to suck fluid and air out of the chest. They are removed when they are no longer required to drain air or fluid.

The external end of the drain is placed underwater, creating a seal to prevent air from flowing back through the drain, into the chest. Air can exit the chest cavity and bubble through the water, but the water prevents air from re-entering the drain and chest. During normal respiration, the water in the drain will rise and fall due to changes in pressure in the chest (described as “swinging”).

 

Last updated May 2021
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