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Diagnosis of lung cancer

Early lung cancer detected on CT scan (left panel) and after treatment (right panel)
Early lung cancer detected on CT scan (left panel) and after treatment (right panel)
The doctor first performs a chest x-ray and if this shows anything suspicious he will run a CT scan of the chest. The analysis of the sputum for abnormal cells is the next test (sputum cytology) and is a very accurate diagnostic tool if positive, and this is usually the case if the patient is coughing up blood; it is less often positive otherwise.


If the tumour is not diagnosed by the sputum cytology, the doctor orders a bronchoscopy (a test where a telescope is manipulated down the throat into the wind-pipe (the trachea) and into the bronchial tubes to directly see any tumour arising from the walls of these tubes.


It is worth noting here that almost all lung cancers are bronchial cancers and arise from the walls of these bronchi. When the tumour is seen or an abnormal area discovered at bronchoscopy, the doctor will take a piece of tissue (biopsy) from this area for subsequent analysis down the microscope for a certain/pathological diagnosis.


If the tumour is not easily seen down the bronchoscope and a single lung shadow on the x-ray could be a birthmark (hamartoma etc.) then a PET scan is useful. This is a functional scan which is ‘hot’ when there is tumour there in the lung but ‘cold’ when the chest x-ray abnormality is one of any of the lung benign shadows which include congenital hamartomas or scars from old injury. If the result is equivocal or PET scan positive and the lesion not able to be biopsied on bronchoscopy, then a transthoracic fine needle biopsy directed by CT is diagnostic in most cases.


The message from all the above is that the diagnosis of lung cancer has to be made from sputum cytology or biopsy (which is down the microscope). Sometimes the patient presents with spread of the cancer outside the chest and then the diagnosis can be made from biopsy of a metastasis, e.g. an abnormal lymph node in the neck.

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