Clinical Assessment and Initial Tests
If a person presents with symptoms such as a persistent cough, shortness of breath, chest pain, or blood in the sputum, the doctor will begin with a clinical assessment:
- Reviewing symptoms, medical history, and risk factors such as smoking and occupational exposures.
- A physical examination that may include spirometry to measure lung function and blood tests to rule out other causes such as infection.
Chest X-Ray
A chest X-ray is generally the first imaging test. According to the NHS, most lung tumours appear as a white or grey mass on a chest X-ray. However, it cannot definitively diagnose lung cancer because it cannot distinguish a tumour from other conditions, such as an abscess or pneumonia. If a chest X-ray raises concern, the patient is referred to a chest specialist for further investigation.
CT Scan
A CT scan is the next step. It produces detailed cross-sectional images of the lungs using X-rays and a computer, with contrast dye injected beforehand to improve image clarity. A CT scan better characterises the size, location, and nature of any abnormality, and can identify enlarged lymph nodes. It takes 10 to 30 minutes and is painless.
PET-CT Scan
If CT confirms a suspicious finding, a PET-CT scan may follow. This combines positron emission tomography with CT imaging. A mildly radioactive material is injected beforehand, so that cancer cells absorb it at a higher rate than normal tissue, making them visible. PET-CT is especially useful for identifying whether and where cancer has spread, and takes 30 to 60 minutes.
Biopsy - Confirming the Diagnosis
Imaging cannot confirm a cancer diagnosis. A biopsy (laboratory analysis of a tissue sample) is required. The method depends on the tumour's location.
Bronchoscopy
Bronchoscopy is used for tumours in the central airways. A thin, flexible tube with a camera is passed through the mouth or nose into the airways. The doctor visualises the tumour and takes a tissue sample under local anaesthetic with sedation. This procedure typically takes around 30 to 40 minutes. An endobronchial ultrasound (EBUS) variant combines the bronchoscope with an ultrasound probe, also allowing sampling of central lymph nodes.
CT-Guided Needle Biopsy
A CT-guided needle biopsy (percutaneous biopsy) is used for peripheral tumours. A needle is passed through the skin and guided by CT imaging to the tumour site, where a tissue sample is withdrawn under local anaesthetic.
Thoracoscopy and Mediastinoscopy
A thoracoscopy or mediastinoscopy may be needed in more complex cases. Thoracoscopy uses small chest incisions to access and sample tissue under general anaesthesia. Performed under general anesthesia, a mediastinoscopy involves a brief hospital stay to examine the lymph nodes and central chest area.
Liquid Biopsy
A liquid biopsy is a newer, minimally invasive option that analyses circulating tumour DNA in a blood sample. It is not yet a replacement for tissue biopsy, but it is increasingly used to complement diagnosis and monitor treatment response.
Staging
After lung cancer diagnosis is established, staging determines how far it has spread. For NSCLC, clinicians use the TNM system. T stand for tumor and it describes the size and local extent of the tumour; N describes lymph node involvement; M tells whether the cancer has spread to distant organs. These values combine to produce an overall stage from I (localised) to IV (metastatic). For SCLC, a two-stage system is used: limited-stage (confined to one side of the chest) or extensive-stage (spread beyond the chest).
Biomarker Testing
For NSCLC patients, biomarker testing on the biopsy tissue is a critical step before treatment begins. The tumour is analysed for genetic mutations, including EGFR, ALK, ROS1, and KRAS, as well as PD-L1 protein expression. These results determine whether targeted therapy or immunotherapy is appropriate, both of which can offer significant advantages over chemotherapy alone for eligible patients.
Conclusion
The diagnosis of lung cancer starts from imaging tests, like X-rays and CT scans, followed by a definitive test, like a tissue biopsy, for confirmation. Once a final diagnosis of cancer is established, staging with the help of PET-CT scans can determine how much the disease has spread using the TNM system. In some patients, biomarker testing can identify specific genetic mutations to guide personalized treatments, such as immunotherapy. This approach ensures that doctors can move quickly from diagnosis to treatment plan.
